Hi,
thank you for reporting back, and sorry for my belated answer.
This is unfortunate indeed: On some IPFire installations, Squid seem to behave odd no matter which additional components are enabled or disabled. I continue to be out of ideas what happens here - sorry.
Will do some testing and experimenting over the course of the next few days, in the hope of somehow reproducing that problem… 
Sorry to disappoint, and best regards,
Peter Müller