MATLAB: Matlab doesn’t have same rights as user

Question

I'm sitting on a fresh installation of 2015b on windows 10. For some reason, I can't write to the Documents folder from inside matlab? My user has ownership of the folder, and both administrators, the user and SYSTEM has "full control". Running matlab as administrator does not change anything. I can edit files in Documents from other programs (or, at least wordpad) with no problems. The result is the same whether I try editing existing files, or saving new ones. Apparently, matlab is still able to write to the desktop folder, but I can't see what the difference between the two locations is.

any ideas?

edit: more precisely, I can not, from within matlab, write to C:\Users\kaare\Documents\MATLAB or C:\Users\kaare\Documents\

("kaare" being the username)

my current work-around is to save pathdef.m to the desktop, and then move it manually to C:\Users\kaare\Documents\MATLAB\

further edit:

here is the result when I try to perform the same operation from the command line, instead of the gui:

>> savepath
Warning: Unable to save path to file 'C:\Users\kaare\Documents\MATLAB\pathdef.m'.
You can save your path to a different location by calling SAVEPATH with an input
argument that specifies the full path. For MATLAB to use that path in future
sessions, save the path to 'pathdef.m' in your MATLAB startup folder. 
> In savepath (line 204)

Answer 1

It turned out that the problem was caused by my antivirus, which included a "ransomware protection". Adding matlab.exe as a trusted program for that module solved the issue.