We found bug in CBCGPTabWnd during tab swapping. Tab window is not reflecting on message WM_CAPTURECHANGED. It can happen that window lose mouse capture without receiving WM_LBUTTONUP (e.g. during OLE activation).
Thank you for the bug report! This problem is already solved and fix will be available in the next library release (6.75, will be released soon). BTW, the problem is not related to WM_CAPTURECHANGED message. If you wish to receive a fix now, please write firstname.lastname@example.org.