Can't save changes to file in NFS share

I can create and delete a file in the NFS shared folder. I can erase text from a text file in the NFS shared folder, save it, and the changes persist. I can change the file name. But if I try to add text to a text file in the NFS shared folder, the added text disappears once I close the file and re-open it. Yes, I saved it. The Linux machine accessing the NFS shared folder is Linux Lite 3.8 (based on Ubuntu 16.04 LTS). NFS shared folder permissions are: Owner: root (root); Access: Read & Write; Group: root; Access: Read & Write; Others: Read & Write. I'm logged into the Linux machine as <marc><password>. OMV version 3.0.99. OMV users are root - admin for the control panel.