We create a matrix job, which has one of the axis as such:
"test-124 | -m a,b"
"test-125 | -m w,z"

In the job's shell script we cut the 2nd half and turn it into our parameters for our application.
This fails to create a proper URL for the job.
Full example (note the "-m%20rc,d%20" - this is the issue):
http://example.com:8080/view/View/job/HaComb_Snapshots_Test_Suite_Coverage/CMD=x5290_MP_FC_sym50_rcd1+rcd2_raid+on_SnapBackupTest_sas%7C-n%20sym50%20-m%20rc,d%20-r%20--dcbtest%20SnapBackupTest%20-g%20sas,label_exp=sustain&&single&&snap&&BoazS/

Simple workaround we've used is convert all commas to underscore and later in our script re-set them to commas.