I did a little more testing with seriesfinale to try to find clues that would help jrocha solving these little bugs.

On an empty database, if I had the series 'Fringe' or 'Bang goes the theory', everything works fine but I can't delete the show (but I can delete episodes, mark them, etc...).

If I add another show which title contains an '&' character (like 'Law & Order'), both shows appear with the same title (in my case 'Fringe' for both shows).
If I look inside the second 'Fringe' series, I see the 'Law & Order' seasons and episodes.
I can neither delete 'Fringe' nor 'Law & Order'.

At this point I should probably enter a formal bug for seriesfinale, but I can't remember if (and where) there is a way to do it for maemo apps.