So, I had this happen to me in a game earlier this week, but I just now repro'd it properly.

1) start on team 2 as twitch
2a) push first two top towers down
2b) level to 6 and select pray and spray.
3) start in the top side jungle just NE of the last turret (the one in the base)
4) activate pray and spray
5) attack tower (I threw a clairvoyance next to it so I could see it without walking up to it.)

Notice that twitch will stop just outside the wall and start firing via pray and spray. Notice also that the tower is not taking any damage because the pray and spray range is falling short of the tower.