I made a post on this a while ago, because of people queuing as tanks or healers when they are actually DPS...
If you end up with 3 dps in a group it will not allow the group to re-queue unless 1 of them ticks healer or tank again, which is a bit broken. It shouldn't allow a DPS to tick tank or healer to begin with :/
They might not be ticking the wrong option, the group finder itself is buggy in that regard.
I queued for Story Mode EV with a pre-formed group of 7 people (missing 1 healer). I was a Commando dps, and verified that my group finder settings specified DPS only, Heal was unchecked.
When we queued, I was flagged as a healer, and the group finder added another dps instead.
So we declined, I double-checked my settings, we regrouped and queued another time. Again it flagged me as a Healer.
hope the Monday night patch fixes this.