Facebook usage of mobile data when WIFI is on and available

[mv426hemi]

I have noticed that my phone is using large quantities of mobile data early in the morning (while I'm still asleep) and the phone is connected to WIFI. Doesn't make sense! So that begs a couple of questions:

1) Why is Facebook channeling its data draw through mobile data instead of through the available WIFI?
2) What the heck is Facebook using that data for (we are talking about up to 1/2 Gb of data at a time?
3) How can I stop it from doing that, either by redirecting the data transfer through my WIFI, or stop it completely other than by logging out of Facebook? A follow-up to this question is: When I sign onto Facebook then to start the day, will it simply start the massive data usage then (through mobile data), thusly rendering my turning Facebook off, a wasted effort?

I have turned background data off in my phone settings.

Thanks in advance, and any insight would be helpful!

 

[Tim1954]

That's when fb is taking all your personal details so they can snoop and sell it to the highest bidder.
Not sure about the droid, some phones have an aggressive switch so if the WiFi isn't strong, the device will switch to network... That would be my guess. That's usually in developers options.
You also have a "boost" function which will use both WiFi and network simultaneously for large transfers. That's in networks and connections.
Data saver functions are good if you have that. You can throttle data usage in a few ways. Some apps have settings within the app...
Sounds like you may need to explore a bit and choke this data hog!