Mantis works via sessions, not option propagating within form posts. If you have navigated somewhere else, e.g. in another tab, it will use the settings for that. I just tested and it was okay so long as I worked on this basis.

Okay, still getting the same result and I'm not navigating anywhere else. I mean the Composr main website is still open in another tab but the actual link is missing the filter when I click page 2 without navigating anywhere else. Page 1 has it every time.

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(Click to enlarge)

Thanks for pressing on it. I didn't see the exact link you used, I thought you were being vague about using the filter manually. It's now fixed.

After fixing I saw it is this issue https://www.mantisbt.org/bugs/view.php?id=11569

Thanks.