Strangely behaving 16c

[jebem]

I have a few 11C and 15C's, but not the 16C (not yet...), and have been lucky so far.

In your case, it seems that some memory cells are not able to store information.

I have read some reports elsewhere concerning malfunction when using depleted batteries, but also when using fresh batteries (!).

I would try first with fresh batteries (1.5 Volt per cell), and then look for some depleted batteries (1.3 Volt per cell) and see it makes a difference.