Fractional beam/beamlet direction incorrect

Issue type

Engraving bug (incorrect score rendering)

Description with steps to reproduce

1. Add 6/8 time signature
2. Add a 16th rest followed by a 16th note on any pitch. Continue this rest/note sequence through the rest of the bar.
3. Select the bar. Properties --> Note --> Beam --> Break inner beams (8th)

Expected behavior: the fractional beams (the short second beams indicating the 16th value) should extend from the stem toward the beat they "belong" to. In 6/8, if we consider each 8th note to be a beat, then each of these 16th notes is on the "and" of the beat; thus, each fractional beam should extend LEFT from the stem toward the 16th rest falling on the beat.

Actual behavior: all fractional beams, except for the last on in the group, extend to the right.

Notes:

• I'm filing this as an engraving bug based on advice in the forum. It's my assumption based on what I've read there that this is a bug rather than a style choice or user error. Please correct me if I'm wrong.
• Gould citation FWIW: p. 157 "Fractional beams"
• It seems to me that the Time Signature Properties menu should be affecting how this beaming appears, though I'm not certain. I have tried ungrouping and regrouping all three values (quarter, eighth, sixteenth) in many combinations, all with zero effect on the fractional beaming.
• The issue is not limited to 6/8—that's just the score I'm working with.
• Note that in my example above, it's acceptable for that first 16th to either (a) have an "incomplete" beam left (though it should be both beams, not just the 8th note beam), as my steps to reproduce show, or (b) it could break beam left, in which case it's OK for the fractional beam to extend right. See Gould p. 158.

Supporting files, videos and screenshots

MuseScore screenshot with notes with incorrect fractional beams marked in red:

Finale screenshot with fractional beams extending in the correct directions:

In which versions of MuseScore Studio is this issue present?

OS: macOS Tahoe (26.0.1), Arch.: arm64, MuseScore Studio version (64-bit): 4.7.3-260608135, revision: github-musescore-musescore-cf9860c

Regression

I was unable to check

Operating system

macOS 26.0.1 Tahoe

Additional context

No response

Checklist

• This report follows the guidelines for reporting bugs and issues
• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible