Another plasma 5 bug I don't know where to report

[Mitch Golden]

My son and I have accounts on my laptop on which I am testing plasma 5. 
Both of us are able to log in an use the machine.  However, if he uses it 
- and doesn't even have to do anything - when he logs out the process 
kwin_x11 does not end.  In fact, after I log in, it continues to run and 
pegs one of the cores.  It does not die unless killed -9.

Where should I report this bug?  I don't know what packages are involved.

   - Mitch