Whenever I hold CTRL and click on a tab whilst already on it, it's visibility toggles back and forth.
Goes back to normal when I open a new tab or go to a different one.

@EukalyptenHD This is actually a bug with the toolkit TabView, so I filed an issue report with them, so we can wait on the fix. I'll incorporate it as soon as they release the fixed version.
Of course, I could have played this one off as a feature. ;) In all seriousness, I am currently attempting to fix this. Since this bug seems to only be noticeable to a small number of users, I'll demote it to low-priority for now.
This bug is fixed in master now with commit b304f53e73e9ecce067cd6bfa81c2b98c5464b92