I believe you have found Intuit's latest bug.  I believe someone posted the same "unexpected behavior" yesterday  Intuit needs to buy another can of Raid and spray the place down.

I updated on the 15th, I dont have any trouble opening the checklist.  Im going to run another update right now and see if that screws it up for me too.

EDIT:  No more updates found.

Id try running REPAIR Updates from the Updates drop down menu, and see if that helps at all.