There shouldn't be.
As you probably know you use two vlans, one on either side to avoid an STP loop.
The fact that one of the vlans is in a VRF shouldn't make any difference as far as I can see especially as a VRF is a L3 concept anyway.
So traffic should enter the IPS from one vlan and leave on another.
Should say I have never used a vlan in a VRF in this scenario but can't see how it could create a loop.
Jon