Bug. The order of equipping Rings might affect DPS

I notice that if you equipping two rings in different order, the tooltip DPS are different. It happens to some rings only. Most of my rings don't have this behaviors. My friends also tested their rings and observed this issue as well.

In the video, I removed all my items, disable archmage and didn't take Pure Power(2% lightning damage per 10 int) to try to isolate factors.

https://youtu.be/91vDPcZUmUY

The cast speed is the same but the damage per hit is different.