[margro]

I'm aware that some people have problems with empty recording file names or URLs. Unfortunately I still have no clue what the problem is.

Could you upload the log files from the TV Server and a debug XBMC.log file to e.g. Dropbox or pastebin (if it fits..)
With debugging enabled in XBMC, do also a PVR database reset. This to make sure that the log file contains a backend recording list request.
After that reset, try to play multiple recordings.