did boss 2 and 3 in LFR in a previous group (joined mid way) and then solo queued for the first boss, killed it, left the raid and had 30 minute deserter buff.
This is intended now, if you leave any LFG content without completing it entirely you will recieve the deserter debuff.
The update only mentioned dungeons, not raids, so I think it was improperly applied to all LFG content.