Somewhat related: trying to add a breakpoint in a class function (e.g. in an @... folder), the same prompt comes up. Adding the folder to the path does allow stopping at the break point, but then the class may have defined functions which will shadow others. That can become a mess.

Work around: after adding the folder to the path, and setting the breakpoint, the folder can be removed from the path and the breakpoint still works.

Doing the same for files in private folders doesn't work and the breakpoints are (eventually) cleared if the private folder is removed from the path.

Octave can obviously find these files (class or private functions), why can't break points be set and caught in them?

If I try to debug a file in a private folder, by setting a breakpoint in the gui by clicking in the margin, I get a dialogue box "Change Directory or Add Directory to Load Path", with options to "Change Directory", "Add Directory to Load Path", or "Cancel". Changing the directory isn't an option, and Cancel won't mark the break point in the GUI. Adding to path allows the breakpoint to be set and can be verified to have been set by using the dbstatus command. However, the debugger won't stop at those breakpoints. The file can be stepped into and stepped through (whether or not the private folder is added to the path), but dbcont will not stop at the breakpoint.