Mu follower tube rush

Hi, I have designed two phono amps both using 6072A tubes. One has a cascode first stage passive RIAA and a common cathode second stage. The other the passive RIAA is sandwiched between two mu followers. Using the physically same tubes (plus one for the MF) I get a high level of tube rush with the MF design that is not present on the other. Same PSU is used for both. Anyone have any ideas why this is the case? 

thanks
Jessica