exception 0xC0000005 PostgreSQL 9.1.6 on Windows Server 2008 R2

Yesterday (and twice today) we got this from pg_log:

2012-10-04 14:29:08 CEST LOG: server process (PID 1416) was terminated by exception 0xC0000005
2012-10-04 14:29:08 CEST HINT: See C include file "ntstatus.h" for a description of the hexadecimal value.
2012-10-04 14:29:08 CEST LOG: terminating any other active server processes

Version string is: PostgreSQL 9.1.6, compiled by Visual C++ build 1500, 64-bit
OS version: Windows Server 2008 R2 (6 GB memory 64bit)

This has started occurring after upgrading from 9.1.5 AND adding a plpgsql function "log_insert()" (tables and function appended).

Application log suggests a an exception during a rollback is occurring:

2012-10-04 14:29:08,322 [26] Log ERROR ***** - Error in LogClass.Insert(). Cause: Object reference not set to an instance of an object.
Stack Trace: at Npgsql.NpgsqlCommand.ClearPoolAndCreateException(Exception e)
at Npgsql.NpgsqlCommand.GetReader(CommandBehavior cb)
at Npgsql.NpgsqlCommand.ExecuteBlind()
at Npgsql.NpgsqlTransaction.Rollback()
*snip*

Removing the use of said function from application seems to have removed the issue.
I have tried replicating it on a similar setup to no avail :(. Hence the appended script will not guarantee an exception (in fact I can't get the exception from other than live environment)
The live environment has around 1500 databases and on average 10-20 open connections.

I hope you can shed some light, but I understand this is too little to go on for a proper investigation.

Kind regards
Bo Thorbjørn Jensen