I think you have mistaken the camera zooming to avoid clipping with the environment with your fingers controlling the zoom. Unless there is some secret zoom gesture I'm missing.
pjmlp
The game is the one mistaking it, all happens with single finger movement.
One second it is going forward, sundenly the next second zooms in.
maplethorpeOP
Well perhaps you are experiencing a bug since mine only does that when there is an obstacle in the way of the camera.