A dialog opened over another must run the replaced one's close callback first

Fact

A UI with one dialog slot usually stores the open dialog's onClose and runs it from close(). If open() simply overwrites that slot, a dialog opened while another is showing replaces it without its cleanup ever running: whatever the first one changed when it opened (a camera, a mode, a timer, a canvas being drawn into) stays changed, and no dialog is left that can undo it.

Why it matters

It looks like a corner case until a dialog does not block the page. A see-through dialog or side sheet (pointer-events: none on its backdrop) leaves every other button that opens a dialog clickable, so "open while open" is an ordinary click, and only at the screen sizes where those buttons are neither hidden nor under the panel. The symptom shows up later, on another screen, as a state nothing on it explains.

How to apply

• In open(), take the current onClose, clear the slot, then call it, all before building the new dialog. Not after: the new dialog may set up the very state the old cleanup resets (opening the same dialog again is the simple case), and a cleanup run afterwards undoes it.
• Calling close() from open() works too, if its other effects (a sound, returning focus, re-enabling input) are harmless in between.
• Test it with a real pointer click on an opener beside the open dialog, at a size where one is reachable: [[element-click-does-not-hit-test]].