The Camelot Herald announced that the doppelganger invasion seems to be slackening off...another way of saying that the current 'adventure' with doppelganers is coming to an end:

Eyewitness reports indicate that fewer and fewer Doppelgangers have been spotted recently in the Frontiers. It appears that the actions of intrepid adventurers throughout the realms have helped to beat back these ancient foes! Scholars remain cautious though and still request that any Doppelganger pieces that adventurers find be brought to them for further study and appropriate reward. They want to be ready should this retreat be nothing more than a strategic recoup leading into a more calculated and devious attack in the future.

(Note: The current phase of the Doppelganger Invasion event will be ending soon. The quest-givers will remain after the event to redeem any current Doppelganger parts that players have, but the Doppelgangers will cease to spawn, in their current incarnation, in roughly a week.)

Get in on the adventure while you still can.