Yes, as you are using the loopthrough from your Fortec star to supply the signal to another receiver you will get this problem
In order for loopthrough to work properly, you need to turn OFF the first receiver, else it will maintain control of the LNB, and won't let the 2nd receiver get a look in.
Some TPs will work;the ones that are on the same band and polarity as the first receiver was on.
Normally, receivers only have to be in standby to relinquish control of the LNB, apart from
Sky digiboxes, maybe the Fortec Stars operate similarly to the digiboxes in that respect.
Remember a UNIVERSAL LNB is a switched device controlled by the receiver, the polarity and band needs to be selected.