Rated 5 out of 5 stars

If you use the Customize Header functionality to remove all the buttons (Reply, Archive, Delete, etc) - and then collapse the Header - there's a strange different-colored "box" of space where the buttons would go.
With the Header expanded normally, everything is fine. No weird box. But if you collapse the Header (and don't have any of the buttons on there) - then you see it. sohbet

This review is for a previous version of the add-on (1.1.4). 

Could please describe the exact way you got this bug:
Did you do a fresh installation?
Which operating system/TB version/CompactHeader version?
Any messages in the error console?
Do you use the single/double line compact header view?
Did you close the customization dialog before toggling the header view mode?

You should see this dark area as long as the customization dialog is open but not afterwards.

Does it go away if you press restore default set/display at least on button?

Could please give your details at the support thread on mozillazine:
http://forums.mozillazine.org/viewtopic.php?f=29&t=1405155

A screenshot might be very helpful.