Deleting the cab_xxxx files only results in regeneration every 30 minutes.
Checking <windows>\Logs\CBS folder, you'll find lots of .log and (some) .cab files.
It seems that windows wasn't able to zip (makecab.exe) one of the .log files.
Solution is:
in <windows>\Logs\CBS folder delete the log files
in <windows>\temp folder delete every cab_xxxx
in the following regeneration process, the remaining (CBS) logs are zipped correctly, and <windows>\temp is left clean