Consider this scenario:
Make a file with several, not-facing pages e.g. 100*100mm.
Change the first page dimensions: Select the first page, click on 'Spread Setup...' select 'current spread' radio-button and enter e.g. 120*100mm. Press OK. The spread is resized as expected.
Now, 'remember' you actually wanted to resize all of the spreads in this publication. Not just the first one.
No problem. Back to 'Spread Setup...', select 'All spreads' radio-button, glance at the dimension input... alright... it says 120*100mm. Press 'OK' button and expect all spreads to be resized to 120*100mm.
Scratch your head. They did not.
Now, if user explicitly reenters the same dimensions that are already set in input boxes, the spreads will get resized. Therefore, it seems that Publisher is waiting for dimension input box edit in order to apply the change, but ignores the user input user commited on radio boxes. Perhaps an improvement would consider change/edit in radio boxes as user input/intent, too.
Affinity Publisher Beta 126.96.36.199. on Mac