Is this issue not fully resolved (unstable solution) as of version 2.4.0?
I ran into issues today when this caused my intended way to resolve a step-up job failed me when BleedBox didn't add nothing outside the TrimBox size. The size of the placed page did increase, but nothing was added outside the TrimBox size, despite bleed being set up.
To resolve it I tried exporting as PDF's from Designer, but the result was then that the content stretch rather than reveal what's in the bleed area when I switched from TrimBox to BleedBox.
Ended up resolving it by using Acrobat to remove an element (CutContour frame) from each page in the original file supplied by the customer, instead of opening it in Designer, removing those elements and using the designer file in Publisher.
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I actually made sample files to test, that failed as well.
A pure 50mm square with 2mm bleed and a square that was 4mm larger, only being revealed when bleed was included (BleedBox).
One Designer file was using a 50mm page without an artboard, and the other one with an artboard.
Trying them again later today, it didn't behave as earlier.
Switching from TrimBox To BleedBox seems to behave as expected now.
While earlier the file with the artboard did not behave correctly at all.
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Since it just behaved, I started testing a little more.
Adding a new page in the original Publisher document that didn't behave at all earlier.
This time the test square (from the Designer document with artboard), didn't behave correctly but not as earlier either.
It showed the bleed content, but not fully on the right side.
I inserted it again a second time, switched from TrimBox to BleedBox, and it looks as expected.
Then I zoomed out to do it again, and the bleed content shows in the first square too.
Rolling my "zoom wheel" it seems that some zoom levels don't show correctly while some do.
Attachments show the same test file side by side in different zoom levels.
Only the left one misbehaves.
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Placed the file several more times and it behave our misbehaves depending on the zoom level and if there is any distance to the adjacent ones. I'm starting to think my screen card drivers might be having issues ...
Time for a reebot, to see if that resolves it.