I have two users, 'Chris' (the administrator) and 'Test.User'
I set 'Test.User' to have a 1MB quota and 'Chris' to Unlimited.
'Chris' shares a folder "APAC" to 'Test.User', with the folder owned by 'Chris'
Test.User synchronised 'APAC' to 'C:\Owncloud\APAC' using the client.
If 'Test.User' adds 'ownCloud-126.96.36.19928-setup.exe' to 'C:\Owncloud' then they get the error:
12/06/2017 10:46:04,ownCloud-188.8.131.5228-setup.exe,C:\Owncloud,Continue blacklisting: Error transferring  server replied: Insufficient Storage (Sabre\DAV\Exception\InsufficientStorage)
This is expected.
If 'Test.User' then adds 'ownCloud-184.108.40.20628-setup.exe' to 'C:\Owncloud\APAC' (the shared folder) they still get a quota error:
12/06/2017 10:49:39,APAC/ownCloud-220.127.116.1128-setup.exe,C:\Owncloud,Error transferring  server replied: Insufficient Storage (Sabre\DAV\Exception\InsufficientStorage)
This isn't expected, as it should consume quota from the owner of that shared folder 'Chris'
If 'Test.User' uploads the file to the shared folder via the WebUI, then it uploads successfully - meaning the quota is being incorrectly enforced for the client upload (or the WebUI upload, depending what the actual intended behaviour is).
This is covered in https://github.com/owncloud/core/issues/14600#issuecomment-307678556 but I hijacked a 2 year old thread to work it out, and it probably needs a new bug to be filed.
Tested with 10.0.2