Switch install is tripping the breaker
Pushing your switches back into the box is causing something to short together - your screws, grounds, or any exposed wire sticking out of backstabs (of which there should be none).  

Are you getting intense arc flashes? If you look closely at your screws, grounds, and any exposed wire sticking out of backstabs -- you will probably find arcing marks that will tell the tale.  

If you are not getting arc flashes of any size, this part of the circuit may be protected by AFCI or GFCI. 

To protect screws, wrap the switch or receptacle with electrical tape so the screws are covered.