Cleansing Light (Dawnguard quest)

[BlackPete]

While I was doing "A Daedra's Best Friend, the "Cleansing Light" quest (DLC1RH02) started after killing the master vampire in Haemar's Shame, even though I hadn't accepted that quest from Gunmar yet. Is this supposed to happen? It just seems odd, because I've never experienced that before, but maybe this is the way the radiant quest system is supposed to work in the game.

 

Edit:

When returning to Gunmar, it finished the quest as normal and I was able to get another Dawnguard radiant quest, so I'm assuming this is working as intended.