These are all stories of either SHARES dropping segments or partners cancelling segments after SHARES fails to push updated ticket information over. Does not provide any compelling reasoning for why UA should be unable to process a simple I->O upfare on an existing award ticket. It would've been no problem before October, but it's longer possible with the new UA award policies.

SHARES has a knack for dropping partner segments (especially for airlines which use 1A as CRS), but once a valid ticket has been issued against inventory, the partner airline has no right to cancel the segment. It's only when the segment is dropped and UA tries to resell it on the reservation that the partner has the option to say no.