Export to MIDI or XML issue

Maybe someone knows why and have a solution.

I have Midi tracks, and usually I can export them as MIDI files, but sometimes I cannot - the export option is grayed out. And I'm not talking audio tracks, of course. I don't think there is anything particularly weird on those tracks, unusual time signature with change and tempo, but I would guess this should not be a problem?

I worked around the problem by creating a new track and copying the notes—the option was active on the new track, as it should be on the old one. I can't find a reasonable explanation for why this happens.

[Edited by Moderator]