Hi!

I am recording guitar and bass through a scarlett 2i2.
I notice when I pan the guitars 100% there is still sound in the opposite channel, barely audible, but there none the less.
The track has been bounced to mono.  I have changed my I/O config a hundred times, turned off all fx and amp sims and it's still there.
Did I have the wrong config when I actually recorded?  Seems if it 'sbeen bounced to a mono track then that should not matter.
As always thanks in advance.

I know stereo and mono panning works differently by spec.

If you are in mono and pan all the way, there should be nothing in the other channel. Bypass FX to be sure it isn't stereo reverb or something.

Yep, ALL fx off. I deleted the amp sim from the channel as well.  Just a dry mono channel, no bus, and it wont pan all the way.
My inputs for the channel are Focusrite left - right- stereo, I have tried all 3 numerous times.
Output is set to Master with no fx on the Master bus.

What are your meters showing you when you record/play?
 
Start by checking it's ok at track level, then buss, then master.
 
It's important you do it in this order. And please make sure your track interleave is set to mono, otherwise weird things WILL happen.

I had the same issue with my Presonus Firestudio Mobile.  Great box and inputs for the money. After about two months of tackling the issue, it was retired and is collecting dust (two years ago).  As far as I'm concerned, if I have to spend too much time trying to configure gear, it stays out of my arsenal. 
 
I checked my board, "Windows", and the Presonus app settings.  After I reached my limits, I reverted back to ye ole faithful, my "M-Audio Audiophile 24/96", which I've been using strong since my first purchase of the original "Sonar" in 2000.
 
Good luck!

@OriginalDunga
I totally spend time configuring gear!!
I spend a LOT of time configuring gear.
My guitars.
My Amps.
Pedal Boards.
And the software that comes with my interface is just another part of my gear that needs love.
I re-read the help file for my interface on rainy afternoons like it's a mystery novel and I'm hunting for clues.
 

originaldunga if I have to spend too much time trying to configure gear, it stays out of my arsenal.

this

MetalTeK

My inputs for the channel are Focusrite left - right- stereo, I have tried all 3 numerous times.
Output is set to Master with no fx on the Master bus.

I also have a focusrite saffire. I tried to pan a mono track and also got sound in the muted side of the headphones. I had to go to the master and change the master to mono in order to get a silent side.

I run 2 different Focusrites and never get this problem.
 
But until MetalTek gets back to us, we're just shooting in the dark.

Uhg....thanks a lot everyone.  

I Record on a dry track, no bus with Pan set to 0.  
Output set to Master
Now when I set input to Focusrite "Stereo" the meters only show sound in the left channel, but I can hear residual noise in the right.
When I set input to Focusrite "Right" nothing shows in the meters.
And oddly enough when I Set input to Focusrite "Left", both channels show input.