At what point was there a change in the IMAP response to the UID FETCH command? We have been sending

Code:
UID FETCH <uid> BODY.PEEK[]
since 6.0 and received back

Code:
* 1 FETCH (BODY[] {<body size>}
...<body>...
 UID <uid>)
dutifully. Suddenly a client updates to 8.0.2 HP 2 and we get back

Code:
* 2549 FETCH (UID <uid> BODY[] {5735}
...<body>...
)
for the same request.

What gives? Why the change? This seems to be breaking protocol.