This was an intended change in behavior for 14b to allow users to create accurate breakpoints without needing the file to be on the path.
To change the directory to a given file, use the feature designed expressly for that purpose: right-clicking on the file's tab and selecting "Change Current Folder".
You can also add the file to the path, rather than (or in addition to) setting a breakpoint, by right-clicking the tab with the file name in the Editor and selecting "Add <foldername> to Search Path" . This operation will put the file's folder onto the top of the MATLAB path.
Finally, you can programatically create a script that will add the necessary folders to the path with the "addpath" command and execute this script before debugging your code
Hope this helps!