Why do I have shiny patches where I touched up paint on my walls?
This is a usually a problem with with the sheen differing due to different application techniques.  That is mixing spraying, brushing, and/or rolling.  My guess is the paint was applied by a roller or sprayer, and the touch up was done with a brush.  The sheen between the different application techniques will be different and noticeable.

We usually try to make sure every thing is rolled in some way so we can roll out our touch ups so they hide better.  So when we spray, we back roll a coat or the primer.  Then when we touch up, we back roll all the brushed locations with a low nap roller.  This typically will hide all the touchups very well.