Beams sometimes outside the stems, and sometimes frayed

[henkmosseveld]

I'm not sure why, how and when it happens, and if there's a cure. Most likely it's because of the Lilypond font!

Sometimes the beams reaches outside the right stem. When partial copied (copy measure 3-4 in a new system), pasted and polished, the result looks a little frayed:

When you click the image it's perhaps even more clear.

B.t.w. Polishing and depolishing can change the result: sometimes perfect groups change to imperfect.