Well, I do think that one important factor is that the LTWs _arguably_ don't involve the purchase or sale of a security. Remember the bankruptcy definition of "debt" versus "equity" again - something to the effect of a debt can be exchanged into an equity without consideration (I don't have the information handy right now). In this case, the LTWs are exchangeable into Wamu stock w/o consideration. If we're considered a debt under bankruptcy because of that, almost by definition we can't be class 18.
Almost.
Oh well.