A given frame's dissection can have multiple packets for a given protocol, if, at any protocol layer, a PDU can contain multiple PDUs for the next layer above it (or parts of multiple PDUs, as with byte-stream protocols such as TCP).
Some recent changes have been submitted to fix that for particular protocols.
However, the underlying problem is that frame.protocols is intended to be a set (in which a given item can occur only once) rather than a bag (in which a given item can occur multiple times). Perhaps it should be implemented as a set, with uniqueness enforced, so that individual dissectors don't need to keep from putting another XXXX in the bag if there's already one there?
