I think this existed in a previous version where when you click the dropdown at the end of the filebar to get popup menu list of all the files currently open they were in alphabetical order. I found this made it easier to locate a file by scanning down the list if you have a lot of files open at once.

You can select Alphabetcal vs Z-order by setting Tools->Settings->MDI-style file tab switching. MDI-style means Z-order.

I tried this, by turning off MDI file switching. The drop-down list is still not in alphabetical order. I tried restarting PhpED, verified that the MDI-style file tabs switching was still unchecked, but the files are still not in alphabetical order.

Then I closed all my files, and opened a handful in random order. The drop down is still not in alphabetical order. This is true for both drop-downs, the one under the Window menu and the drop-down arrow at the right end of the tab bar.

This is a loss of functionality. Previously, you could have MDI switching enabled, so that CTRL-TAB took you to the most recently used tab, but the file drop down remained alphabetical. With the Visual file tab switching enabled, you could get a pop-up showing the files in most recently used order. Hence you could easily get the list of open files in either order, without having to change settings. It appears that this is no longer possible.

Both orders are necessary, because they address two different user stories. One helps you find a file when you know you used it recently but weren't paying attention to the name (which happens very often when you're debugging, stepping through functions in a large system). The other helps you find files when you know the name, know that it's currently open, and it's much easier to find than drilling down through the workspace explorer.

(Aside: MDI is, I believe, a concept known to MFC programmers, but far less likely to be recognized by people whose only or primary work is web site development in PHP. It seems like the wrong term to be used to describe this feature.)