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