There's another situation where this can cause problems. If you change the extension from html to php, or vice-versa, you end up with both files in the output - index.html and index.php. Once uploaded, which one gets used depends on the default settings on the server, so it's a gamble.
I wonder which skins allow the user to change the page extension?
All skins, because it is a jAlbum core function.
But I do sometimes a skin change by dropping an already used project file in the image directory. The new project file could have another naming convention as the old project file.
It is a pity that jAlbum supports both htm and html files, I would vote for using always html files.
Ah, so it isn’t a skin issue at all. Whilst I agree jAlbum should be tidier, the manual warns about the effect.
And if you use multiple project files on a single project, well, you run all sorts of risks.