a stem added to a whole note

Hi, in the attached score a spurious stem is added to some whole notes, eg m9, G in Sup II, m15 G in SupI, m22 last note of all parts, m26 last note in 5 of the 6 parts; and more. It turns out that if I move the note up or down, or when I 'x' the note as if to invert the (non-existing) stem, the spurious stem disappears, and in the case of m22 and 26 they also disappear from the notes on the staffs above and below. So I do this, the save and quit. But when I reopen the file, all the spurious stems are there again.

I note that in all cases, these whole notes extend into the following measure and that that feature is experimental. But I use that feature regularly, and though this is not the first time I see this happen, it is rare.

Also, this score is a reworking of https://www.cpdl.org/wiki/images/3/3a/Ramsey_When_David_Heard.mxl, which I imported.

Thanks,
Andrea
(MS4.4.1 on Mac OS 14.6)