Problem with client internal name prefixes

When using client internal name prefixes, odd behaviour can result. As far as I can see, it appears linked to having the same first letter for the client name and the prefix.

I first noticed this with a client named 'cbpq' and a prefix of 'cl-', where the internal name started out 'cl-cbpq', it's now stuck at 'cl-bpq'.

To replicate, add a client internal name prefix (admin/hosting/client) of 'ab-', then try creating a client named 'aaaa'. The resulting client internal name will be 'ab-'!

I'm guessing there's a malformed regex somewhere in hosting_client.