BUG #5504: cache lookup failed for function

The following bug has been logged online:

Bug reference:      5504
Logged by:          Jan Merka
Email address:      merka@highsphere.net
PostgreSQL version: 8.4.4 and 8.4.3
Operating system:   Linux
Description:        cache lookup failed for function
Details:

After installing postgresql 8.4.4 from sources, I am getting an error
ERROR:  cache lookup failed for function 2071

Test case:

> SELECT date '2010-01-01'  + interval '1 month';
ERROR:  cache lookup failed for function 2071

So it seems like adding an interval to date does not work anymore. Why? And
how do I fix it?

I have tried to go back to the 8.4.3 version but it now exhibits the same
problem even though it worked fine until the 8.4.4 version was installed.

What can I do to fix it or help you with fixing?

Thank you,

Jan