Created attachment 121030 [details]
Screen of the bug
Do you have the same problem when using the Windows default theme?
Duplicate of 30891; although that bug only mentions XP, it actually happens with many third-party visual styles in Windows 7, 8/8.1 and (most probably, not yet verified) 10 as well. This issue is not present with the default Windows visual styles.
*** This bug has been marked as a duplicate of bug 30891 ***