Rehearsal marks messing up page layout (solved)

I created a basic single-line drum sheet template for my students, which is perfectly layouted without any rehearsal marks.
When I start to add rehearsal marks to each line (1-8) the layout breaks and puts half of the systems on a second page, leaving the first page half full? That’s weird. Possibly a bug or am I missing something?

I did change the setting for “vertical justification” to “100%”, because I didn’t want Dorico to auto-format the system spacing.

Project File:


When you add rehearsal marks, Dorico makes the assumption that those rehearsal marks are going to push the staves further apart, which in normal circumstances they would do. I don’t have the energy at gone midnight to explain the precise way in which Dorico handles vertical justification, but suffice it to say that it’s complicated, and involves taking into account a number of factors in order to estimate what the likely required height is going to be, which then gets adjusted as further processing is done. Your layout is a bit of a pathological case for this estimation process, as you have more rehearsal marks per page than you would see on average, even in a typical part, so it’s guessing that it can’t fit all the systems on one page.

Fortunately it’s very easy to sort out: simply select the first note on the first system and the last note on the last system and choose Make Into Frame in Engrave mode, per the attached.
Single Paradiddle (175 KB)

Thank you so much Daniel!
I guess I should better use normal text for line numbering on a single exercise worksheet, but I didn’t even think of that, since it’s an automated workflow for many years using rehearsal marks for that purpose. You solved my problem anyway.