Ok... lets try this again...
open 2 or more files in the IDE... 1.c, 2.c, 3.c, for example.
Click the tab for 1.c
(See step 1 attached)
Now go Window -> Cascade ...
Note that the tab is already wrong for the foreground window
(See step 2 attached)
Now click the zoom button on 3.c
Now the IDE is showing 3.c but the tab row is still highlithing 1.c
(See step 3 attached)