BUG #8984: ERROR: t_xmin is uncommitted in tuple to be updated

The following bug has been logged on the website:

Bug reference: 8984
Logged by: Marko Tiikkaja
Email address: marko(at)joh(dot)to
PostgreSQL version: 9.1.11
Operating system: 64-bit Ubuntu
Description:

Hi,

I just noticed we've had the error in subject happen around ten times,
starting from Thursday. I don't see it having happened before that. IIRC
that day we also switched to another synchronous slave. The previous slave
had hot_standby_feedback=on, and the new one has it turned off. Might just
be a coincidence.

All of the failing queries are inside PL/PgSQL functions, most of them are
SELECT .. FOR UPDATE or UPDATE against a table called "workers", but there
are a couple of instances against other tables as well.

Any ideas? I'll be happy to provide more information, just let me know what
you need.