Surprising (for me) Discovery : I have a small book open in Sigil and I right click on the index.xhtml file and edit with Notepad++. Then I save the changes in Notepad++. The changes I just made are
immediately apparent in Sigil - the text in the code view window changes before my very own eyes
I'm sure this is by design, not the sort of thing that happens inadvertently. I suspect we're probably all saying the same thing from different perspectives. I am not sure it's germane to OPs issue, that's why a made my post OT.
Added : it's also what Toxaris said Sigil did. I guess I'd prefer a warning like Notepad++ has. But, I never edit epub component files outside of sigil while sigil has the epub open. I prefer to unzip the epub, do the editing (most often images) and rezip the epub. For no good reason I have a prejudice against deep process trees
Feel free to delete posts 7-10 - over and out.
BR