Odd bug in system break delete

Latest version on Windows 10 (1909 pro).
Pictures are worth a thousand words, so see attached (other blurred for copyright reasons) screenshots.

image “Step 1”: In engrave more I delete the first system break on page 2
image “Step 2”: the whole score becomes modern art.

If I first delete the system break on page 1, then from page 2, all is ok.

The System Break on page 1 is set to Wait For Next System Break (in the properties panel). This property tells Dorico to keep forcing measures onto the same system until it encounters a System Break.
Either insert another System Break, or untick this property.

This property is typically set when you use “Make Into System”. What “Make Into System” actually does is insert two system breaks, then sets the first one to Wait For Next.

All of this also applies to Frame Breaks and the “Make Into Frame” button.

If you imply that this behavior is by design and as desired, then I strongly suggest that Dorico should never get into situation where whole score is crammed into one page, no matter what the logic and reason is behind it.

It certainly is by design, and is often desired. If Dorico’s Note Spacing settings want to put four bars on a system, but (in order to facilitate a page turn) you need to put six bars on one system, this is the mechanism you use to do this. Dorico doesn’t care whether there are 6 bars before the next system break or 6000 bars - it does what it’s told.