Yes, I've been noticing this for the past few weeks. Itineraries on hold that come close to duplicating a confirmed (but refundable for 1Ks) award itinerary are canceled at around midnight of the day the itin is held.

The software is apparently "smart" enough to tell even when a "similar" itinerary is on hold. I've got an award itin and held a similar itin that shares no flights but leaves on the same day. From the same departure city but to a different destination. The software has been catching these, too, and canceling my holds.