I've got a problem with a plugin I'm giving a minor tweak to. The plugin has a couple of masters, one an esm, the other an esp. The change I'm making is minor, simply changing a small amount of text in a message box. After making the change to a script and saving it, the plugin loses the esp as a master, and loses everything that master contained... so it breaks scripts and quests and such. When I open the plugin in the construction set again, if I try resaving the script, I get errors where it's now missing globals and such from assets contained in that master.
What steps do I need to take to be able to edit this plugin without breaking its links to that master file? I'm sure this kind of info has been addressed before, but I just couldn't figure out any good search terms to find it.
Thanks in advance.