Under Ubuntu 14-04, after a system update, Plank does also have this behavior.
Plank version 0.61+bzr1067-0ubuntu1~ricotz1
I have Plank on the right side.
In the process list I can see Plank as running, but it is not visible at startup.
If I start a program which is in the dock, Plank does not show up.
If I start a program which in NOT in the dock, Plank does show up, and stays/works.
I hope, that my description will help in the trouble shooting.
Thank you for the very good program.
Under Ubuntu 14-04, after a system update, Plank does also have this behavior. 0ubuntu1~ ricotz1
Plank version 0.61+bzr1067-
I have Plank on the right side.
In the process list I can see Plank as running, but it is not visible at startup.
If I start a program which is in the dock, Plank does not show up.
If I start a program which in NOT in the dock, Plank does show up, and stays/works.
I hope, that my description will help in the trouble shooting.