After disconnecting from an external monitor(secondary screen), even the primary display goes blank. This gives the user no clues as to what is happening. The worst part is that this problem persists even after rebooting and there's apparently no way to get rid of it.

Reproducible: Always

Steps to Reproduce:
1. Connect to an external screen.
2. Disable the primary screen, keep working on the secondary screen.
3. Disconnect the external screen. 

Actual Results:  
The primary screen goes blank and the problem persists in future sessions as well.

Expected Results:  
On disconnecting the external screen, the primary screen should be active and the user should be able to continue working on it. 

I'm using kubuntu 14.10, unstable ppa : kubuntu/ci . 

I think this is a grave problem, since, without the display, the software is unusable now. There was however a workaround that I was able to figure out, which could be useful. Read here : https://harishnavnit.wordpress.com/2015/01/26/workaround-plasma5-session-fails-to-start/