Psql malloc error on Git master

Using 9.1devel as of yesterday's Git branch master, I'm getting an
error in psql when attempting to tab-complete a system tab.

Steps to recreate:

1) From terminal, run "psql postgres" to connect to the postgres
database as the current user.
2a) Type: \d pg_o
2b) OR type: \d pg_op
3) Press TAB to auto-complete

Result:

postgres=# \d pg_opsql(29265) malloc: *** error for object 0x5:
pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug
Abort trap

I haven't been able to cause this error to happen with any other
prefix. Using pg_opc then TAB does not cause this to occur, neither
does pg_ then TAB. I have also tested this on 64-bit versions of
PostgreSQL 8.4.4 and 9.0.1, and it doesn't occur on those versions.

System info:

OS: Mac OSX 10.6.5
Kernel: Darwin 10.5.0
Arch: 64-bit kernel and extensions enabled
Processor: Intel Core i5 2.53 Ghz
Memory: 2x2GB DDR3 @ 1066Mhz

Built with GNU Make 3.81
GCC version: i686-apple-darwin10-gcc-4.2.1

If required, I can provide the configure output.

--
Thom Brown
Twitter: @darkixion
IRC (freenode): dark_ixion
Registered Linux user: #516935