Recording fine for 2/3 takes, then 4th just...fails

Community, weird annoying glitch I've never seen before. Recording to mono audio track, all fine. After three or four takes, the next take goes goofy. Arm record track, Arm record on transport, hit space bar, cursor moves BUT no red recording on the track. Input signal present and correct, playback fine, but it's as if the track wasnt armed to record (except the Transport would tell you if that was the case). Anyone got a Scoobie? using Fireface with TotalMix; had same problem with Babyface interface.