Problem with pltcl trigger

We have problem with pltcl triggers.
We have table with unique field on which executes a emty pltcl trigger
after update, insert and delete.
Situation is:
1. Starting new seassion;
2. Executing first update query without exceptions;
3. Executing second update query with unique exception;
4. Closing seassion.

Sometimes, when this seasion repeated many times without waiting,
seasion closes abnormaly postmaster process is defunct.
DEBUG log for defunct seasion has only this difference from normal seassion:
--------------------------------------------------------------------------------------------
DEBUG: reaping dead processes
DEBUG: child process (PID 20805) exited with exit code 0
---------------------------------------------------------------------------------------------
And the are no more exceptions or smth.

When trigger is dropped or function is plpgsql seassions closes normaly.
Pltcl triggers would be used later for column changes logging, but this
abnormal situation stops our works.
We try change trigger cal before or after but situation was same.

Our system parameters are:
* debian - kernel 2.4.27-8
* pgsql 7.4.7-7
* tcl 8.4.9-1
* libpgtcl 7.4.7-2

Can you help us in this situation, or give some advice?

Saulius M.