It might be linked to that annoying "beeping" in the background
On-topic: it might be that that "save" button fixes a setting that may went bogus when changing from day to night modus. Saving (an unchanged form) might still push all these values in that form into the memory of that camera, performing a "small" reset, that fixes your symptoms. I'm just wondering, if you would leave your cam all night on night modus, would that flickering start again, automatically at random times? That might indicate your cam is loosing setting parameters, which isn't good. If that's not the case, you might look into calling dahua API to "force" your cam into night mode, with eg antiflickering. See http://<ip>/cgi-bin/configManager.cgi?action=getConfig&name=VideoInOptions with tons of "night" options:
Code:
head.NightOptions.AntiFlicker=0
head.NightOptions.Backlight=0
head.NightOptions.BacklightRegion[0]=3096
head.NightOptions.BacklightRegion[1]=3096
head.NightOptions.BacklightRegion[2]=5096
head.NightOptions.BacklightRegion[3]=5096
head.NightOptions.BrightnessThreshold=50
head.NightOptions.DayNightColor=2
head.NightOptions.ExposureMode=0
head.NightOptions.ExposureSpeed=0
head.NightOptions.ExposureValue1=0
head.NightOptions.ExposureValue2=40
head.NightOptions.ExternalSyncPhase=125
For more information on the API (first google result, no promises here): ftp://ftp.wintel.fi/drivers/dahua/SDK-HTTP_ohjelmointi/DAHUA_IPC_HTTP_API_V1.00x.pdf
Hope this helps!
CC