diff --git a/media_server/services/display_service.py b/media_server/services/display_service.py
index 1fd01fd..0df96ba 100644
--- a/media_server/services/display_service.py
+++ b/media_server/services/display_service.py
@@ -267,20 +267,27 @@ def _probe_static_open(mon, mc, monitor_id: int) -> dict:
     except Exception as e:
         logger.debug("Monitor %d: color_preset unsupported: %s", monitor_id, e)
 
-    # Picture / scene mode (VCP 0xDC) — not exposed by monitorcontrol's
-    # high-level API, so probe via raw VCP transport.
-    try:
-        mon.vcp.get_vcp_feature(PICTURE_MODE_VCP)
-        static["picture_mode_supported"] = True
-        cmds = caps.get("cmds") or {}
-        declared = cmds.get(PICTURE_MODE_VCP)
-        codes = sorted(declared) if declared else sorted(PICTURE_MODE_LABELS.keys())
-        static["available_picture_modes"] = [
-            {"code": c, "label": PICTURE_MODE_LABELS.get(c, f"Mode {c}")}
-            for c in codes
-        ]
-    except Exception as e:
-        logger.debug("Monitor %d: picture_mode unsupported: %s", monitor_id, e)
+    # Picture / scene mode (VCP 0xDC). Trickier than color preset because
+    # many monitors (LG ultrawides included) respond to READS but silently
+    # drop every WRITE - they implement the register but not the feature.
+    # The capability string is the most reliable signal: a monitor that
+    # really implements picture mode declares its supported codes under
+    # cmds[0xDC]. If 0xDC isn't declared, treat the feature as unsupported
+    # to avoid exposing a non-functional select.
+    cmds = caps.get("cmds") or {}
+    declared = cmds.get(PICTURE_MODE_VCP)
+    if declared:
+        try:
+            mon.vcp.get_vcp_feature(PICTURE_MODE_VCP)
+            static["picture_mode_supported"] = True
+            static["available_picture_modes"] = [
+                {"code": c, "label": PICTURE_MODE_LABELS.get(c, f"Mode {c}")}
+                for c in sorted(declared)
+            ]
+        except Exception as e:
+            logger.debug("Monitor %d: picture_mode declared but unreadable: %s", monitor_id, e)
+    else:
+        logger.debug("Monitor %d: picture_mode (VCP 0xDC) not declared in capability string", monitor_id)
 
     return static
 
@@ -498,6 +505,31 @@ def set_power(monitor_id: int, on: bool) -> bool:
         return False
 
 
+def _verify_after_set(getter, expected, *, retries: int = 3, delay: float = 0.1) -> bool:
+    """Poll a DDC/CI getter to confirm the monitor actually applied a write.
+
+    DDC/CI writes are fire-and-forget at the protocol level: a successful
+    send does not mean the monitor honored the value. Many monitors silently
+    drop writes for codes their firmware doesn't really implement (LG's
+    ColorPreset / Picture Mode are common offenders). Without this check the
+    API would report `success: true` while the monitor sat unchanged.
+
+    Compares both raw and `.value` forms so enum/int mismatches don't flag a
+    spurious failure.
+    """
+    expected_int = getattr(expected, "value", expected)
+    for _ in range(retries):
+        time.sleep(delay)
+        try:
+            actual = getter()
+        except Exception:
+            continue
+        actual_int = getattr(actual, "value", actual)
+        if actual == expected or actual_int == expected_int:
+            return True
+    return False
+
+
 def set_contrast(monitor_id: int, value: int) -> bool:
     """Set contrast for a specific monitor (0-100) via DDC/CI."""
     mc = _load_monitorcontrol()
@@ -511,6 +543,9 @@ def set_contrast(monitor_id: int, value: int) -> bool:
             return False
         with ddc_monitors[monitor_id] as monitor:
             monitor.set_contrast(value)
+            if not _verify_after_set(monitor.get_contrast, value):
+                logger.warning("Monitor %d: contrast %d not applied", monitor_id, value)
+                return False
         _invalidate_cache()
         return True
     except Exception as e:
@@ -536,6 +571,11 @@ def set_input_source(monitor_id: int, source: str) -> bool:
             return False
         with ddc_monitors[monitor_id] as monitor:
             monitor.set_input_source(target)
+            # Source switches can briefly disrupt the DDC/CI link; allow a
+            # longer settle window before declaring failure.
+            if not _verify_after_set(monitor.get_input_source, target, retries=5, delay=0.2):
+                logger.warning("Monitor %d: input source %s not applied", monitor_id, source)
+                return False
         _invalidate_cache()
         return True
     except Exception as e:
@@ -561,6 +601,12 @@ def set_color_preset(monitor_id: int, preset: str) -> bool:
             return False
         with ddc_monitors[monitor_id] as monitor:
             monitor.set_color_preset(target)
+            if not _verify_after_set(monitor.get_color_preset, target):
+                logger.warning(
+                    "Monitor %d: color preset %s not applied (monitor silently rejected)",
+                    monitor_id, preset,
+                )
+                return False
         _invalidate_cache()
         return True
     except Exception as e:
@@ -584,6 +630,16 @@ def set_picture_mode(monitor_id: int, code: int) -> bool:
             return False
         with ddc_monitors[monitor_id] as monitor:
             monitor.vcp.set_vcp_feature(PICTURE_MODE_VCP, code)
+            # Raw VCP read returns (current, maximum) — only compare current.
+            def _read_picture_mode():
+                current, _ = monitor.vcp.get_vcp_feature(PICTURE_MODE_VCP)
+                return current
+            if not _verify_after_set(_read_picture_mode, code):
+                logger.warning(
+                    "Monitor %d: picture mode code %d not applied (monitor silently rejected)",
+                    monitor_id, code,
+                )
+                return False
         _invalidate_cache()
         return True
     except Exception as e: