COPY and domains

I noticed that COPY is getting very slow, when importing to table, which
makes use of domains as column datatypes. It seems like foreign key
validation is especially slow. It takes ages to import table with 25000
rows, which has foreign key reference to another table with 25000 rows.
I tried the same tables without domains and it was much faster. Is this
known problem?

Version: PostgreSQL 7.3.2 on i386-pc-linux-gnu, compiled by GCC gcc
(GCC) 3.2.3.

Tambet