Strange audio defect with new FCPX

In a normal Interview I record my audio separately with a clip mic on a recorder, but its mono on only one track. So after synching in FCPX I normally go into the inspector, deactivate the reference audio from the camera and convert the good audio track from stereo into dual mono, to have it on both channels. That worked always with any problems. Since the latest version when I listen to the synched clip, I do have the audio on both channels, but it sounds with a little echo, like if the two audio tracks were one frame out of sync. I tried to redo everything, clicking all the possibilities, but no chance. Is that an issue or am I missing something?

I haven't noticed anything like this, but do report this to Apple.

What happens if you set the Pan mode to Stereo Left/Right instead after you have set the fie to Dual Mono? Normally you should get 2 equivalent mono tracks.

Best wishes,

Ronny