Looks like nothing to do with the character to me. Looks like something provided a path with a trailing \ to something that wasn't expecting it and has pasted its own path seperator on without checking to see if it is needed. This may be a bug in a Windows context where a \ is the default character for a path seperator, but / may be used.

Check any paths that you are handing Tk for trailing path seperators that ought not be there.