Map jumps after specific scale & pan actions

This issue has been migrated from mozilla/webmaker-android#1700.

It was originally written by flukeout on Fri May 08 2015 and had the following description:

Steps to reproduce:

• Place your index finger down and pan the map
• Place your thumb down and pinch to zoom the map
• Release your index finger
• Pan the map with your thumb
• Place index finger down and pinch zoom
• The map jumps

Something about switching fingers triggers this.