svn switch hang (protocol problem?)

I have a WC that is a checkout of a branch. I attempted to switch this
back to head and svn switch ran for a very long time (1.5 hours).
Eventually I straced it and found an amusing dialog between client and
server:

write(4, "( failure ( ( 210001 25:Unknown "..., 4096) = 4096
write(4, "subversion/libsvn_ra_svn/marshal"..., 45) = 45
read(5, " ( 210001 25:Unknown command \'fa"..., 4096) = 4029

I can reproduce this easily, and attach a strace taken from the start (I
hit ctrl-c after it looped for a while). I am using subversion 0.26.0
on client and server. I've kept a copy of the WC that lets me reproduce
this.

-- 
see shy jo