Controllers aren't recorded

I have a MIDI piano part. Now I want to add changes in velocity by recording this over the original part by use of the mod wheel. I hear the mod wheel do its thing while recording and I see the controller being added in the graphics of the track. But when I stop the recording that’s gone and I’m left with the original track, without any added controller action. What am I doing wrong?

OK, I’ve resolved this myself (and I’m so proud). Turns out SysEx was turned on in Preferences - Midi Filter.