The gist of it is that Mudlet plucks out the GMCP content out of the data stream, and processes it, raising all relevant events, before the text processing even starts. As a result, the information of the original GMCP position within the text stream is lost. I have tagged the BUG with a question mark because there is some poor wording (IMO) in the GMCP standard that could lead to confusion. However, I believe the way Mudlet is currently processing the GMCP info is contrary to what the MUD servers expect, and contrary to what other GMCP compatible clients implement, so contrary to at least de-facto standard. This leads to some out-of sync oddities, and breaks some functionalities as well.
- The GMCP event indicating arrival to a new room is generated while the character has not reached the intended destination yet, as based on text output still passing through some rooms on the way there
- Some GMCP info meant to deliver a spoken message from the mob can lead to receiving a mob's speech way before arriving into the room with that mob, and before some mob actions associated with it (like body language, passing an object, etc).
- The original GitHub issue mentions GMCP used for tagging around text info, marking special use of that text (channel communication, map). This type of GMCP signalling is of course completely broken by the way GMCP is processed at present.