TYPO3 Core

This applies to the "Columns" view of the Page module.

Good point.

One "hacky" solution would be to have "unused elements" rows in layouts which have more cells than others, so that all layouts provide the same amount and number of colPos. :)

unused elements should be one "column" in the view then containing all elements that are not assigned to any of the "active" columns

But IMHO this is more a feature than a bug - so it should be ready with 4.6

A column at the bottom of other columns (and displayed ONLY if there's content assigned to a non-existent column) would be IMHO good solution.

I agree this looks more like a feature even though backend layouts currently create a problem which wasn't possible with the previous fixed set of columns.

IMHO it's not a real problem, since the elements already are "unused" in the current state, so they would not hurt in the frontend as long as the FE-setup matches the selected backend layout - which should always be the case of course.

Well, not that it would be a problem in the frontend. It's only a problem for editors who might prefer to work solely with the Page module and a change of layout of a page makes their content "disappear".

In my experience, many of the editors have limited capabilities of working with computers in general and they get easily confused by things like that.

...an administrator might actually not give editors access to the List module at all so as not to confuse them by giving them access to 2 modules that allows them to do the same (I'm talking purely about tt_content editing as many editors actually don't do anything else) in a different way.

In such a scenario editors would "lose" access to the content that "disappeared".

Does anyone know if this has been fixed? Or a good workaround?

The workaround is named "Grid Elements". Installing it will not just provide proper handling of unused elements (by assigning them to colPos -2) but give you a lot of other nice features.

Actually this is not about denied access, but about columns that are just not provided by the current layout - so the elements are not restriced but get lost.
So a column "unused elements" would make sense IMHO. Of course you should not see elements of restricted columns in there, but this is not the case with TV and/or Gridelements anyway.

Well - forget about it - I just missed the point when a simple editor switches to another layout that does not have restricted columns. In that case elements of restricted columns would become visible. Should not be a default feature of the core then but activated on demand i.e. via Gridelements.