Wi-Fi sync is using my internet connection

[rosscommvidler]

Last night I left my computer to sync my locally stored offline playlists with my new phone over Wi-Fi. I was greeted in the morning with an email telling me I have used 10gb of my data allowance. Can anyone please confirm how spotify syncs over Wi-Fi? I was under the impression that the data was being downloaded from my hard drive on my computer to my phone over the Wi-Fi network without traveling via the internet network. I can understand there may be some internet data used to log and cross reference my files butt seems that all the data has been downloaded completely from the spotify servers. Can anyone please clarify how spotify syncs over Wi-Fi. Thanks

[catmoosebear]

I did a quick test for myself which consisted of unplugging the Internet cable from my router, the result is that the files stopped downloading. From this i've gathered that at least some Internet connectivity it required to transfer songs from the computer to your device. and considering that you've seen then same thing from the opposite side (device using unusual amounts of data) its likely that using this music download /sync / file transfer feature  is done completely though the Internet. 

hopefully local area networking file transfers become a reality and until then i'm not going to be using this service as I have a data cap on my home Internet

edit: 

I just monitored my network connection to see if my cellphone was communicating with any download servers, and i didn't pick up  on any communication that wasn't directly from my computer to my cellphone or vice-versa, unfortunately this contradicts what you have experienced.

Definitely more interested in the answer now

edit 2: 

it is good to note that after downloading a couple of songs onto my cellphone they are locked into the spotify app and i can't use them elsewhere (ringtones, alarms, notifications) while this doesn't relate to the question at hand its definitely something i wish i knew before starting all this