I ran into an interesting bug today. I had a struct with a field whose id was greater than could be represented by in the delta space. The protocol specifies that when this occurs, we follow the type byte with a varint that contains the actual field value.
The problem comes in that when we go to the varint, we don't pop the previous field id value off of the stack, leaving it in place for the next operation. Sometimes, this probably doesn't even cause a problem, as if it's the last field in the entire serialized data, it won't get in the way.
Both the ruby and c versions of the protocol seem to be affected by this issue.