I have not been able to reproduce this is in UE4 or CSS Form Builder 2.
I currently have about 20 pages open in Dreamweaver, from about 9 different sites, and others are from support issues on the forum, and using the DW Edit icon in UE is not clearing the settings for me.
I'll continue to experiment to try and find the cause, but I'm glad to hear you have discovered this work around.