BEGIN-cascade blocks application

It's
PostgreSQL 7.3.4 on hppa-hp-hpux10.20, compiled by GCC 2.8.1

I'm having a ported monitoring application using the libpq interface.
After running well for several hours it surprisingly stopped
without any error condition.
The application was blocked completely.
After re-start it worked as expected.
I've turned on statement logging to find out
about the last one being processed. It was
BEGIN;
WARNING: BEGIN: already a transaction in progress

It was the last of a cascade of duplicate BEGINs,
and the only reason I could see for the application being blocked
was this cascade. I eliminated those duplicates and now the
application runs without any stops.

Was it my fault?
>From reading the manual I was not aware firing duplicate BEGINs
(ok, there were probably several thousand, but not uncommitted)
could have such an drastic effect.

Regards, Christoph