Sound outage when recording on MacBook Air, [moved from General A/V] Options

[HydrogenOxide]

This is a strange problem when recording music via an interface:

When I am recording sound (Amadeus Pro) via a bus-powered firewire-S/PDIF-interface (Weiss NT) having my 2012 MBA on battery, and during recording I plug in the power cable, there is a complete zero input for one second or so (shown as -infin dB). Mostly it goes with digital artefacts. Sometimes this also happens when doing other commands while recording, but the most reproducible problem is when plugging the power cord.

Possible reeasons: 

Core Audio goes down?
Power for the external interface goes off?
....?

I never had this problem with my earlier MBP and SL. 

Anybody?