[Bug] ...

(mCtrl-0.11.5) debug, 64bit, gcc compiler, Windows-64bit
Occurs at the moment of tab movement, this is unhealthy behavior.

[codygray]

It's not clear what issue you are trying to report. Is the problem the color splotching in what should be a gray background?

This is obviously a custom application that you have written and are using to host the control, since the title bar says "ProportionalTextEditor". Can you reproduce this with the bundled "example-mditab" and/or "example-mditab-dwm" sample applications? I cannot. If you cannot reproduce this with the bundled sample applications, please post your code that reproduces the problem.