Just installed 1.5.1_... on an Ultra 1, and everything seems OK,
		except for a marked tendency to drop into DDB when ^C is hit on
		a process (not necessarily on the console). Is this an 'upgrade'
		to -current issue?

Probably.  What's the reason for entering DDB?

ISTR there is debug code in the kernel to detect attempting to enter
the signal trampoline with either an invalid pc or invalid stack and
enter DDB.  That usually happens before the address space is fully
set up.  You should be able to get rid of that behavior by not using
DEBUG kernels.  But in either case, -current should not have that
problem.

Eduardo