64bit tx frame is being sent by XCTU as a 16bit frame - why

XCTU software alters frame type and length
Frame generator used to produce a 64 bit address TX frame
Frame is transmitted and received at the end point but is 16 bit address with the checksum altered to match the shortened frame. Any ideas why XCTU does this and how to prevent it

Yea, set your MY on the transmitting module to 0xFFFF.