I came across the same issue.
The only way to add Jabber to the video conference with other Telepresence endpoints which use H264 was to set Conference Legacy level from 0 to 1 (or higher).
However, this made things looking ugly in Jabber although video with continuous presence started to work.
Seems to me it happens due to some issues with MCU transcoding or custom video format Jabber uses.
Please, write back if you've found any viable solution to the issue with MPS.