Calling ROUND w/o a numeric cast blowing up all connections (9.1)

I don't know why this is happening, but it's infuriating. From the psql
prompt:

mydb=# select round(5/2, 1);
SSL SYSCALL error: EOF detected
The connection to the server was lost. Attempting reset: Failed.

This kills any connection to the database. Doing 'round(5/2::numeric, 1)'
works fine.

Version: PostgreSQL 9.1.7 on x86_64-unknown-linux-gnu, compiled by
gcc-4.4.real (Ubuntu 4.4.3-4ubuntu5.1) 4.4.3, 64-bit

Nothing shows up in the log.

Have I broken my cast function? My round function? Have I angered the RDMS
gods? Can anyone give me any pointers?

--
Wells Oliver
wellsoliver(at)gmail(dot)com