Draw Sign will not select the correct level for the sign panel state level symbology. Shouldn't the existing to remain and remove sign panel cels come in on SignPanel_ep level so that they display in dashed? Mine constantly come in on SignPanel, which is a solid linestyle.
Have you tried setting the Sign Panel Level Symbology, found under FILE>PREFERENCES in the Draw Sign Program?
When I override the symbology, it reverts back when I close Microstation.