E,Eb, or D on impulse bypasses kontakt

I have noticed my vsti Kontakt is being shut off for some reason when I hit one of the following three keys: E,Eb and D just above middle C on my Novation Impulse 61 keyboard. I can't think for the life of me why it would do this. Hitting middle C then re-engages it. So if I hit one of the three notes above kontakt sound stops immediately. Is there a simple way to fix this? I want to play without kontakt shutting off.

Does this happens only with a particular library or it happens with anything you load in kontakt? When you mean it's being shut off you mean it's muting it own output channel or it simply doesn't make any sound?

+1, which instrument shows this issue? I reckon that they are key-switches of some sort. Does the product manual say anything about those keys Also, can you record the MIDI when you press those keys and a few others, just to make sure all is OK there?