Perhaps we should alter the wording slightly to clarify what's happening when opening/saving or when manually executing Mend? I can see how it might be a bit confusing to some. Maybe "Attempt to Fix XHTML Errors on Open" or something?
Or... since it seems that many of of Sigil's other main features (Save [if Mend on Save is checked], Rename, Split, Merge, Restructure, etc...) will trigger the entity substitution/preservation anyway, can we just make Mend on Open behave like Mend on Save does regarding entity preservation?
I have no idea what that would entail--and I'm certainly not trying to cause extra work--but there would be a certain symmetry/logic to Mend on Open/Save following the same roadmap RE entities when checked/unchecked, no?
In case that's not clear what I'm suggesting is:
1) Mend on Save/Open - handle entity preservation/substitution based on whether the option is checked or not in Preferences (that's how Mend on Save behaves now, for what it's worth)
2) The manual Reformat HTML->Mend would continue to behave as it does.
That's all "if possible" of course.