Ugh... It looks like there is no way to disable that property once it is enabled...
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/shellcc/platform/commctls/tab/reflist.asp
Specifically, the property that Mark appears to have enabled for the tabs is "TCS_HOTTRACK", which causes whichever tab the mouse is hovering over to be highlighted blue.
The only way to fix this would be to create a tab control manually. But I'm not sure if that would work with Blitz's event system or not.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/shellcc/platform/commctls/tab/reflist.asp
Specifically, the property that Mark appears to have enabled for the tabs is "TCS_HOTTRACK", which causes whichever tab the mouse is hovering over to be highlighted blue.
The only way to fix this would be to create a tab control manually. But I'm not sure if that would work with Blitz's event system or not.