I have made a clock using the schematic below to run 8 segment displays. There are 6 of them. All the displays share the same ground, which then goes to the n-MOSFET (bottom right of the schematic), which can dim all the displays via PWM from an Arduino.

I am also using the clock for other purposes. I noticed that when I illuminate the DP (via the 470 ohm leg of the UDN2981 - Out 8) on any one of the displays, all the displays show faint lighting of their unlit segments. This only occurs when the PWM from the Arduino is low (ie the display is dim), not when the PWM is high(ie display is bright). 

I cannot figure out why this would occur, and how to stop it. Any help would be greatly appreciated. 

[![enter image description here](https://i.stack.imgur.com/waqKS.jpg)](https://i.stack.imgur.com/waqKS.jpg)