Hikvision 2142 Config Frustration

I'm using a DS-2CD2142FWD-IS dome camera and it seems like a great product but I'm having one strange and frustrating problem.

I've got the camera working on my network using PoE and talking to my D-Link NAS via FTP. I've also got email notifications working. I've configured motion detection, intrusion detection and line crossing functions working and I receive emails when they trigger.

BUT, my frustration is that the camera will ONLY send pictures to the NAS at night, or more correctly...

Hikvision 2142 Config Frustration