diff --git a/README.md b/README.md
index e98078b..8867480 100644
--- a/README.md
+++ b/README.md
@@ -9,14 +9,15 @@ product ID or have a K87 layout, so the keyboard is ignored without this plugin.
 Copy `Womier_K87_EVision.js` to `%USERPROFILE%\Documents\WhirlwindFX\Plugins\` and restart SignalRGB.
 
 The device settings have a "Key test" option (column or row sweep) to check the LED map,
-"Low frame-rate mode" in case the keyboard drops frames at full speed, and a "Frame rate limit"
-(Unlimited / 30 / 15 / 10 fps). Known issue: single keys occasionally flash a random colour for a moment.
+"Low frame-rate mode" (normally not needed) and a "Frame rate limit" (Unlimited / 30 / 15 / 10 fps).
 
 ## Protocol
 
 - HID interface 1, usage page `0xFF1C`, usage `0x92` (collection 4), 64-byte output reports.
-- Colour frame: packets of `[0x04, sumLo, sumHi, 0x12, len(56), offLo, offHi, 0x00, ...56 RGB bytes]`,
-  where the checksum is the 16-bit sum of bytes 3..63. 7 packets cover LED slots 0..127.
+- Colour frame: packets of `[0x04, sumLo, sumHi, 0x12, len, offLo, offHi, 0x00, ...len RGB bytes]`,
+  where the checksum is the 16-bit sum of bytes 3..63. The plugin uses len 54: 7 packets cover LEDs 0..125.
+- The keyboard shows each packet as it arrives, so `len` must be a multiple of 3. With the stock
+  plugin's 56, LEDs 18, 74 and 93 (W, O, Menu) are split across packets and flash random colours.
 - The keyboard falls back to its own effect when frames stop, so colours must be streamed.
 
 ## LED map
diff --git a/Womier_K87_EVision.js b/Womier_K87_EVision.js
index 5abdf87..1133784 100644
--- a/Womier_K87_EVision.js
+++ b/Womier_K87_EVision.js
@@ -24,7 +24,7 @@ export function ControllableParameters() {
 		{property:"shutdownColor", group:"lighting", label:"Shutdown Color", description: "This color is applied to the device when the System, or SignalRGB is shutting down", min:"0", max:"360", type:"color", default:"#000000"},
 		{property:"LightingMode", group:"lighting", label:"Lighting Mode", description: "Determines where the device's RGB comes from. Canvas will pull from the active Effect, while Forced will override it to a specific color", type:"combobox", values:["Canvas", "Forced"], default:"Canvas"},
 		{property:"forcedColor", group:"lighting", label:"Forced Color", description: "The color used when 'Forced' Lighting Mode is enabled", min:"0", max:"360", type:"color", default:"#009bde"},
-		{property:"lowFPS", group:"lighting", label:"Low frame-rate mode", description: "Sends smaller packets with pauses in between, can improve stability", type:"boolean", default:false},
+		{property:"lowFPS", group:"lighting", label:"Low frame-rate mode", description: "Sends smaller packets with pauses in between; normally not needed", type:"boolean", default:false},
 		{property:"frameLimit", group:"lighting", label:"Frame rate limit", description: "Maximum frames per second sent to the keyboard", type:"combobox", values:["Unlimited", "30", "15", "10"], default:"Unlimited"},
 		{property:"keyTest", group:"lighting", label:"Key test", description: "Sweeps a white line across the keys to check the LED map", type:"combobox", values:["Off", "Column sweep", "Row sweep"], default:"Off"},
 	];
@@ -57,8 +57,8 @@ const vLedPositions = [
 	[0, 5], [1, 5], [2, 5], [6, 5], [10, 5], [11, 5], [12, 5], [13, 5], [14, 5], [15, 5], [16, 5],
 ];
 
-// Highest LED index is 125; 128 slots = 384 bytes = 7 full packets of 56
-const LED_SLOTS = 128;
+// Highest LED index is 125; 126 slots = 378 bytes = exactly 7 packets of 54
+const LED_SLOTS = 126;
 
 export function LedNames() { return vLedNames; }
 export function LedPositions() { return vLedPositions; }
@@ -118,7 +118,9 @@ function sendColors(overrideColor) {
 }
 
 function writeRGBPackage(RGBData) {
-	const bytesToSend = lowFPS ? 48 : 56;
+	// Must be a multiple of 3: the keyboard shows each packet as it arrives, so an LED split
+	// across two packets briefly flashes a mix of its old and new colour
+	const bytesToSend = lowFPS ? 48 : 54;
 
 	for (let offset = 0; offset < RGBData.length; offset += bytesToSend) {
 		const data = RGBData.slice(offset, offset + bytesToSend);