This is dependable from K2 and I think their support would be better to ask in this case, but when I'll got an access from You requested in Your other thread, I'll take a look into this as well.
After switching to Protostar feedburner keeps sending full articles. This means problem is not template related and I honestly do not know what can be causing it without a closer look into feedburner's code, unfortunately I'm not allowed to do that. Sorry