I believe there might be more to the problem than just during the Grab Bag sale.  The Grab Bag sale was listed as 10/30 through 10/31. However, after a quick check of my purchases I see that on 10/25/2014 I purchased an item I had previously purchased on 09/27/2013.  (I'll submit a separate e-mail to the address mentioned for requesting store credit later today).

For a variety of reasons these last couple months have been a blur for me.  And I feel like I've caught myself almost repurchasing items a number of times because they weren't tagged as Purchased and not just over the last few days.

Rather than disabling duplicate purchase warning during certain promotions, perhaps the web site could leave the "Add to Cart" button functioning and add an additional banner indicating the item had been previously purchase. 

Basically, uncouple the "Purchased" warning from the "Add to Cart" ability.  That would remove the need to change behavior during Grab Bag or other special promotions.

It's something to consider. 

And I do want to add a Thank You to all the staff and volunteers who work to address our issues.