aki009, welcome to FlyerTalk! Can you give the readers of our United forum some more information about this in order to provide informed discussion: the origin city, the connecting city for the transfer, and the connecting time available would help evaluate whether this does represent a change in United policy. Thanks, Ocn Vw 1K, Moderator.
Update: see this recent thread about a single-ticket itinerary ORD->LAX (United) connecting to LAX->SIN on SQ. Apparently SQ needed to see the traveler's passport before issuing a BP in LAX. Unclear whether luggage was accepted in ORD for transfer to SIN on the SQ segment.
Conflicting Information from United with Connecting to SQ