I have crosstalk set up, so when I enter my flight plan in the IFD100

on my ipad,  it shows up on both my 540 and 440.  When I make changes

to the flight plan, or change com frequencies, or nav frequencies those 

also show up on both radios simultaneously.  Things seem to work well.

I wanted to practice with just the 440, simulating failure of the IFD540.

I powered off the 540  to just use the 440 with the IFD100.  First I could not

connect the IFD100 to the 440, even though the LIO_wifi showed up and 

my ipad said it was connected.

Next, my CDI showed reverse sensing as if I was flying a localizer back course.

Then my approach LNAV/VNAV  didn't sequence at the FAF to the last leg.

All of this worked correctly when performed in Dual IFD operation.

I have a feeling this is all because crosstalk was still enabled in the 

setup menu....which is only accessible on the ground.

This may just be an academic exercise, unless one loses the primary IFD.

I'd be interested to hear if anyone else has tried this  or other insights.

Bob