Adding a "Network Monitor" widget to a panel results in a constant high CPU usage by the plasmashell process.

Reproducible: Always

Steps to Reproduce:
1. Add a "Network Monitor" widget to a panel. In my case I have two panels and two network interfaces (ethernet and wi-fi).
2. Open System Monitor and look at the plasmashell process CPU consumption.


Actual Results:  
plasmashell constantly hogs ~75% CPU core.

Expected Results:  
The process should not consume that much CPU.

I'm using Kubuntu 15.04 x86_64, KDE packages installed from ppa:kubuntu-ppa/backports. There are two panels: one with the task manager, the other is with the app launcher, a few application icons, spacer, System Load Viewer and the system tray. No other widgets on the desktop.