It has always been the case that Glk didn’t really understand the idea of multiple displays. (That is, one game can open multiple Glk windows. But you can’t make several games that each open their own set of windows.)
Desktop interpreters have to do a dodge around this in order to open several games at a time. Traditionally, they fire up a hidden sub-process for each game. And that works fine.
I’ve written up notes on how I would change Glk to support multiple games “for real”:
github.com/erkyrath/glk-dev/wik … ay-Support
This is a low-priority project! The CSS display work is more important. I just wanted to write up this plan to get it out of my head.