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.