Typeidentifying not working sometimes?

Hi,
When I try on current:
abr=> select sum(endt-begt-pausen)/count(*)::float8 from tage;
ERROR: Unable to identify an operator '/' for types 'timespan' and 'float8'
You will have to retype this query using an explicit cast
but:
abr=> \df
...
timespan |timespan_div |timespan float8 |divide
...

Why? Directly used I get:
abr=> select timespan_div(sum(endt-begt-pausen),count(*)::float8) from tage;
timespan_div
-----------------------------
@ 11 hours 24 mins 34.79 secs
(1 row)

It seems that an entry for '/' is defined:
grep timespan_div catalog/*.bki*
...
catalog/local1_template1.bki.source:insert OID = 1585 ( "/" PGUID 0 b t f 1186
1186 1186 0 0 0 0 timespan_div - - )
...

Any clues?

Bye!
----
Michael Reifenberger
Plaut Software GmbH, R/3 Basis