The value does not change, it stays the same as number. The dropdown will show "all" when items in the grid mach the page size exactly. But not if they are less or more.
For example: if you have 1000 records, and you set PageSize = 10. Then filter such way to leave only 10 items, you will end up seeing "All" in the dropdown, because the page size is 10 and the items are 10.
I understand it could be misleading for your clients, if this is the case, remove the "all" option, and place some big number in the dropdown, or disable the paging.
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