There are a couple of other things I can add about this.
As tulamide mentioned, Construct warns about the resolution of the every x milliseconds condition. However, it's generally not even good to 10ms resolution under the default settings. Under the application settings, "Framerate Mode" is set by default to "V-Synced", which effectively limits the resolution to 1/60 (or 16.667 ms) on my computer. It lags on mine until I set the increment to 17 or more.
It's actually close to keeping up with the 1ms increment if I change the framerate mode to "Unlimited", where I get a framerate of around 2800. In practice, I've never felt the need to go below 50ms for any such condition, myself.
Also, I've found it to be a good practice to not rely on exact equality checks for counters such as what you use here. You would notice that it breaks if 1000 is not a multiple of the increment value (as with 17.) I would usually use:
+ System: Is global variable 'MillisecondsB' Greater or equal 1000