I was playing with ITA Matrix and found a LHR-KUL direct round trip on MH, not EoE permitted based on the fare rule.
However, when I added a US domestic flight at the end, the return MH leg merged with the US domestic flight to share a fare code.
The booking class also bumped up from O to N which I initially thought was to make it less restrictive, but when I read the rule, EoE remain non permitted.
Base fare increased but YQ dropped.

Have you guys encounter anything like this? It made me rethink the potential loss of opportunities by giving up on non combinable candidate fares.

Update: The new fare code of the return leg ends with MY instead of GB. Is the system treating my KUL-LHR as the outbound flight now?