[INRAD] Roofing filter and IMD?

[Floyd Sense]

I was looking at a receiver test matrix at w8ji.com today and noted that 
the FT1000MP MK V with Inrad roofing filter tested 13 dB worse for 2 KHz 
IMDR than the same transceiver WITHOUT the roofing filter.   Anyone know 
why that is?  Here's the URL of the subject chart: 
http://www.w8ji.com/receiver%20IM3%20sorted.htm

Is there a problem in the design of the transistor amp used in the filter?

73, Floyd - K8AC