Do you know if/where there is a discussion of the positions of each Senator with regard to each proposed amendment, and the vote on the final bill?
My first impression (my first impressions are often crap) is that some Senators were in favor of the unamended bill (in favor of a flavor of lawsuit immunity), voted for extending the AWB and for the Gun-show provisions, then turned on a dime and didn't want to buy the package deal that they voted in favor of.