Anomalous(?) behaviour opening musicxml file

I have an xmlfile that I have generated programmatically. From the note point of view it consists of 5-note chords e.g. :
G408half1C508half1E508half1E408half5C408half6G408half1C508half1E508half1E408half5C408half6

Because of information in the input file, which is an xmlfile exported from MuseScore4, there are 3 voices 1, 5 and 6. When I try to open it with MuseSCore4 I get a message that the file is corrupted with details like : Incomplete bar: Full score, bar 1, stave 1. Found: 4/2. Expected: 1/1.

If I edit the file so that all voices are 1, then MuseScore can open the file and it is displayed as I would like, but obviously all notes are Voice 1 which is not quite what I want.

If edit the file so that all the non-voice-1 voices are changed to 2, then I get the same errors opening with MuseSCore4. If I open the file with e.g. online soundslice all versions of the file open successfully.

In response to the error message I tried adding some explicit attributes like time, but it makes no difference.

Is this behaviour a bug or a known limitation of MuseSCore4?

In the appended files, the first is the file with multiple voices and the second where all the voices have be changed to 1