Open a project. Make visible the accents toolbar. Detach it. Close TXC. Reopen it, the detached toolbar is still here. Close it with the X button or by unchecking Accents from the popup menu of toolbars. Close and reopen TXC. The detached toolbar is still here.
The only method to make it disappears is to undetach it dragging it to the main toolbar area, then unchecking it from the toolbar list.
I'm convinced to have already opened this bug (without the final partial resolution), but I'm unable to find it anymore. Sorry.