System spacing is inconsistent above a vertical frame
Using V2.0.2 on Windows 7. In the attached score, each page is absolutely full; increasing the height of any vertical frame by 1sp will cause a page to overflow. But the spacing of systems above and below the frames is inconsistent. The issue seems to be related to how music margins are applied.
On Style > General > Page, "Minimum system distance" and "Lyrics bottom margin" are both set to zero so that systems will pack tightly for this example. This can be seen on pages 1-3 and 7-9. Pages 7-12 have lyrics added to show the problem still occurs when "Lyrics bottom margin" overrides "Minimum system distance". "Music top margin" and "Music bottom margin" are both set to 13sp; more about that below.
On pages 4-5 there is extra space between systems, even though the frames are as large as allowed. Pages 10-12 also show extra space between systems, though again the frames can't be made larger. The issue seems to occur whenever a page has two or three systems on top and a page-filling vertical frame at the bottom. (Occasionally, extra space appears with a vertical frame on top and two or three systems below, but not in this example score.) Pages 11-12 show the issue is consistent whether the frame occurs between measures or is appended at end of score.
Note that when there are three systems above the frame (pages 4 and 10), the gap between systems is smaller than when there are two systems above the frame (pages 5 and 11). Comparing frame sizes between pages 1 and 4 and between pages 2 and 5, a total of 13sp of extra space has been added to both pages 4 and 5. Similarly, comparing pages 7 and 10 and pages 8 and 11-12, a total of 22sp has been added to pages 10-12.
The 13sp added to pages 4-5 is the same as the music margins I set in Page style. Before I changed those values from the default 7sp, the extra space on pages 4-5 was also 7sp. I haven't been able to figure out how all the different margin values interact, but this formatting issue definitely seems related to music margins in some way.