lsof on t64u 5.1b - no info for PIDs > 65535

Hi managers--

I'm seeing strange behavior on some but not all of our 5.1b boxes when
running lsof--it returns output fine for lower-numbered process IDs, but
nothing for higher-numbered ones (I'm guessing 65535 based on
experimentation). Other servers run fine. The lsof version is 4.77, and
I've tried all the normal stuff (/proc is mounted, etc.) with no
success. Anyone seen this and have a pointer to a config change or
something?

Happy holidays to all.

--Russ