It seems as the plugin can't trigger a specific configuration inside a matrix job. I have a CI trigger job set up to build a specific permutation of a multi-config job, such as
MasterBuild/BRANCH_NAME=MyBranchName,BUILD_TYPE=Dev,PLATFORM=MyPlatform.

When starting to type in the "Projects to build" input box it even fills in the parameters. However, when the job is triggered I get this:
ERROR: Build aborted. Can't trigger undefined projects. 3 of the below project(s) can't be resolved:
> BUILD_TYPE=Dev
> MasterBuild/BRANCH_NAME=MyBranchName
> PLATFORM=MyPlatform

It seems as the comma sign in the branch is used as a delimiter, thus making three trigger calls. Is matrix job triggering not supported? Can it be extended with say a checkbox for "Invoke matrix project", which would use a different delimiter (semicolon maybe)?