Okay, it seems the issue is more subtle. Scenario :
1. Open freshly unzipped rsrc0009 project, then open the HTML\IDR_HTM_WELCOME in eng.rc by double-clicking on it
2. Modify html, save it, close that window. Note: the BOM is removed from the .htm file.
3. Reopen the resource IDR_HTM_WELCOME by double-clicking on it, it displays funny. You may do it several times, same behaviour every time.
4. Close the window.
5. Edit manually the .htm file with another editor, add the bom, save. Reopen IDR_HTM_WELCOME.
*it stills displays funny*6. Close and re-run Pelle's C, redo step 1, now it displays correctly. Update : it also works if simply closing the project or the eng.rc window and reopening it, no need to close the IDE.
So for sure, if there's a bom at the beginning of the file, saving the resource should leave that bom in place, for consistency. But it should not be added if there was no BOM in the first place. That's one thing. But also it looks like there is like a flag somewhere that's not updated properly when reopening a resource that has been modified in parallel with another editor (I think it's just not reloaded at all actually).
That's my best guess. Note that the bug is not high priority, there are workarounds. But it is disturbing when you do not expect it. Your body starts to shiver, for no mere mortal can resist the evil of Pelle's C ! HAHAHAHA...