Toshiba has moved onto my list of manufacturers not to buy from. I'm fairly sure this is an actual software bug, but I'm sure not seeing any support.
Update: apparently Toshiba technical support is simply incompetent. They told me they duplicated the problem on their recorder and that it was by design, an interesting design concept. I posted about this problem on the AVS forum where one of the members commented that he was able to do more manual recordings than eight on his older Toshiba DVR. I tried adding a couple of manual recordings. This apparently reset the eight item limit so that I'm now able to store more than eight scheduled recordings.
Fascinating. We'll see if all of the schedule is still there tomorrow. It's survived a couple of on-off cycles that I tried as an experiment.
But it sure looks like a firmware bug.