signal CONT not being received/delivered?

this started happening sometime last week, and still with 5.3-STABLE (?) SMP
(haven't seen this on a UP system), the scheduler is SCHED_4BSD.

after su, typing suspend will stop the su but the csh process does
not resume, sending - from another tty - a CONT signal gets it out of stopped

ie:
x-dev# suspend
(hitting ^T)
load: 0.05  cmd: csh 793 [suspended] 0.00u 0.01s 0% 1732k

now from another tty: kill -CONT 793 and it's back to normal.

anything i can do to help debug this?

danny