Let me clear some of this confusion(or add to it), if a Clip already resides in the track and you press play it doesn't do any thing but play whats on the track and not the clip in Matrix right i.e it doesn't restart the clip in Matrix.
That is the way it works it will not jump back on the timeline only move forward and play what is on the track and overrides the Matrix. You need to make sure the cell the matrix clip is using is on an empty track.
What you need to do is to start with an empty project load all of your cells and record that performance. Once you've done that you can't go back and change that performance dynamically, you have to start a new project or record over the one you just did or add a new track corresponding to the Matrix cell you are trying to trigger..
It's a one shot performance tool(using the "Record Performance" button in the Matrix), if you want to change anything after a performance you have to start over or do another project once the performance is recorded to the timeline.
You can't mix and match it's either all in the Matrix or the recorded performance plus added tracks later or a new empty track corresponding to the Matrix cell. Once a track is recorded you cannot change it dynamically with out recording over your previous performance.
I hope that help's to explain the Matrix system enough to understand how you can use this tool.