Exporting Piano as MIDI File

After creating some piano music in MuseScore, I exported the whole file. But only the treble material was exported. I tried selecting only the bass staff. But only the treble material was exported. Finally I cut all the treble staff material and exported the file. Then the bass material made it. I am using MuseScore 4.4.4.243...
Is there any way to make the file export either as two files, treble and bass, or as a unified file, treble+bass?