It is neither possible to reorder tabs nor move then to a new window any more in Arch Linux with Xfce. This is only a problem when using e10, non-e10 works as intended. Problem started within the last 14 days. Works on OS X, so it seems to be platform specific.
Probably a dupe of bug 1212733
staffan.runnsjo, thanks for reporting this bug! If you would like to follow the progress of the fix, you can CC yourself on bug 1212733. Guilherme, thanks for finding the duplicate bug.