slave rendering 1.47/1.5

Hello all,
just installed 1.5 in the middle of a job - always dodgy! Anyway, managed to get everything going across network. I inadvertently left an old version on a PC with backburner server running. It is actually calcualting part of an IR map without throwing any errors!!? Is this right? Do I not need to bother installing 1.5 slave renderer if a previous version is on??
Thanks

better to have all in unique versions
since 1.4x has a lot of been chanced and the render will be very different to 1.5
I am pretty sure the GI map will be to brighten and not work

I seriously hope not. I’ve upgraded so I can move from Scotland to London office with Dongle and network render the IR maps across 50 machines for 9 sequences over the entire weekend!