A picture says more than 1000 words:

Folder: "Scooby Doo Wo bist du" (engl.: Scooby Doo Where Are You)
Filenames: scdwb-01x11, scdwb-01x18, scdwb-01x19, ...
Preferences: TheTVDB (EpisodeMode), Opportunistic (MatchMode), German (Language)
FileBot already renamed from 01x01 to 01x10 totally correct, but you can see 01x18/19/20 won't work this way.
Is not only the filename relevant for finding the title? If it is, why FileBot maps a 1x18 to a 1x01? Makes no sense to me :-/
greetz
eusi
P.S. Tested on FB 4.5.6 and latest (4.5.7b1), Win7 (x64).