I'm not too sure how useful or in demand this feature might be.  It would be handy to have a couple check boxes for .5 pixels on the inside X and Y mirror.

What I found is that when you mirror you have two rows of pixels that will be the same.  This happens on the far right Y and the bottom X.  I think having a "Make Mirror Edge .5" check box for both X and Y could be handy so that you only have one row of pixels in the middle.

I actually ran across this when I was doing that 3D conversion.  Again I am not sure how handy this feature would be.  But for those looking to detail a bit more, it could be cool.

@Moblyn I too have needed this feature and it's already in the next build.

Instead of .5 pixels, its simply an option titled 'disable mirror on center line'.

This option will disable mirroring the center line of pixels either on the X or Y axis.

So if you had an 8px wide grid mirrored, it would end up 15px wide without the center line duplicated.

Will hopefully get this build release in the next week or so!

Rad man, your solution sounds better.

Update v1.2 now out with this feature included.