Dead automation tracks

Has anyone else experienced this?
Sometimes after saving and closing a perfectly normal working project and reopening it, one or more automation tracks are moved to the bottom of the track list, appear grayed out (both the track itself and the options in the track list), and on the original track(s) you can no longer open any new automation tracks.

If you select the dead track at the bottom and choose “Remove Selected Tracks” the original audio track can get new automation tracks, but these too get the same grayed out state.
Clicking the name area of one of these new tracks and selecting “Remove Unused Parameters” removes the track, after that, no new automation tracks can be opened.

Closing a project corrupted this way throws a normal “A serious error has occurred…” with a reference to a log file. When opened, no new entry is made and when deleted no new log is created. (!?)
Forgot one thing: if you remove all the dead auto-tracks as mentioned above, the project can be saved, closed and reopened without errors. The error box only appears if you try to close the project with dead tracks present.

I have not yet been able to work out exactly how to get to this problem starting from scratch, but will try as soon as I get the time.

So, clues anyone?

Cubase 5, Win XP SP3
Pentium D 3.6 GHz
Nvidia GT240
RME Fireface 800