Cursor positioned incorrectly when all characters selected

[sferguson12]

If all characters in a masked field are selected and the user presses cursor left, the cursor is bumped one extra position to the right of the leftmost masked character. For example:

(800)555-1212 => Select all => Cursor left => Cursor is positioned after the 8
123-45-6789 => Select all => Cursor left => Cursor is positioned after the 1

This appears to be related to how the isAddition property is getting set in eventHandler(). I'm using v1.8.7.

The issue is illustrated here: http://codepen.io/sferguson12/pen/LbwrOZ