start button hover bug

I'm getting some very strange hover behaviour with the windows start button. When I'm in some programs (Google Chrome, Firefox) if I hover over the start button and then move my mouse off again, it remains highlighted. If I alt tab to a different program the issue stays until I Ctrl+Right Click on the task bar at which point it works as expected. As soon as I make Chrome (for example) my active window again, the same thing happens.

As I said it only happens with specific applications (So far the only ones I've found are chrome and firefox). Internet explorer doesn't have this effect so it isn't browser-wide. It might be to do with the fact that chrome and firefox both put tabs inside the top bar (alongside _ □ x).

It's a weird issue and hard to explain properly so I'll put a link to a video.

It seems to be an issue with the "disable topmost" option, as it only occurs when that is enabled.

Here's a video anyway:
https://drive.google.com/file/d/0B-eMrpFqN80YU2xDVGptdmFxNms/view