I use Opera 30.0.1856.93524 on Huawei Honor 3C.
Yesterday i suddenly my Opera experience a spike of background data, almost 10GB large! I didnt download anything ,i didnt stream anything. Heck, i barely even used my phone. You can see in the screenshot below that the spike is significant so that it could be considered abnormal.
http://s8.postimg.org/cm5ccbcf9/Screenshot_2015_07_11_13_59_34.jpg