Sorry, there doesn't seem to be a location to post critical bugs, and this seems more important than StackOverflow.
I found a critical XML bug. On orders.xml, on the note attributes, you originally had <note-attributes><note-attribute>… it's now <note-attributes><note_attribute>…, note the underscore. Many of our orders didn't get whatever the customer note said because of this XML bug.
(Meta Question: Is there a place to post this? It seems like StackOverflow is more for "How do I do X?" to have people help each other. There doesn't seem to be a location for critical bugs.)