As you can see it is a titlebar buttons/glyphs issue that has been around for several years. I tried excluding Thunderbird from being skinned, but all that does is make all the titlebar glyph images disappear completely, non-functional. I am on Windows 7 Ultimate, 64-bit and using Windowblinds 10.7 Beta, but this issue has been around in many prior versions of Windowblinds. Doing a purge and reinstall of WB (after unloading WB first) makes no difference. If I apply the Windows Aero skin, the problem goes away. I have just learned to live with this bug, but I thought I'd at least ask about a fix. Thanks.