[Exim] Using $perl from router

Hi,

Sorry, this question has probably been asked before but I think I have a
problem with exim 4.10 and want to check. I want to create a router
that has a condition that is dependent on a $perl call, something like:

my_router:
driver = accept
transport = local_delivery
condition = "${if eq{${perl{myperl}{$local_part@$domain}}}{doit}
{yes}{no}}"

But if I do this then exim crashes with a SIGSEGV in init_perl.
Changing the condition to 'condition = "yes"' doesn't crash.

Is this something you simply cannot do (due to a bug in 4.10 or missing
functionality?) or is it being me being dumb!?!!

Appreciate any help as this is pretty urgent.

Matt