I believe you will have to revert to the workaround to force stereo operation. When you patch a plugin SONAR first tries mono and then finally sets it to stereo on a stereo track. It is the state transition that goes to mono first that this plugin misbehaves with.
I passed it on to Line 6 with a full description of the issue. However they are probably afraid of fixing it in case it breaks other hosts :) Chicken and egg.