pg_relation_size locking

Until recently, pg_relation_size used SearchSysCache to locate the 
relation to examine, and calculated the file location from that 
information. Starting with dbsize.c V1.5 (committed after Beta2), 
relation_open(.., AccessShareLock) is used. This is very unfortunate 
because it will not allow to observe a table growing while it is 
populated, e.g. with a lengthy COPY; pg_relation_size will be blocked. 
After reverting to 1.4, everything was fine again.

Can we have this reverted/fixed?

Regards,
Andreas