Inconsistencies when working with images with different DPIs

[Piolie]

Normally, I scan at 300dpi, but for pages that have very fine details that I'd like to preserve I might switch to 600dpi. Today I found that some settings are mismatched when images with different DPIs are used.

I'm attaching two sample PNG images. One is 1004x812 (300dpi) while the other is 2008x1662 (600dpi). There is nothing special about each image. I just took them from a book in the public domain and saved them with the GIMP.

Below are the steps to reproduce the issue.

1. Create a new project and add the two files.
2. Press the ► button for the steps 1-3, so that orientation, splitting and deskew are handled automatically. (ST will split each page in two.)
3. In Select Content of the first page choose Page Box -> Manual (don't change any value).
4. Press Apply to ....
5. In Options select Apply page box and in Apply to select All pages. Press OK.
6. Select the 3rd page and notice that the page and content boxes have been scaled by 2.
7. Try changing the value of the page box to 42,2 by 64,5. The page box will grow accordingly.
8. Go to the 4th page and return to the 3rd. Notice that the page box has been shrinked again. This happens no matter how many times we try.
9. For our changes to persist, we have to either move the page box with Shift+LMB or resize it with the mouse cursor.

Also, margin guides added in pages of one DPI value are misplaced in pages of the other DPI value. This makes it impossible to align all the pages. Furthermore, the guides position is corrupted when switching between those pages.

OS: Windows10. ST: 2019.8.16 Early Access (64 bit).
Issue173.zip