emberjs/ember.js — pull request #4761 by hjdivad (2014-04-23 19:32:07+00:00)
Title: [BUGFIX beta] reduceComputed detect retain:n better.

Fix #4620.

reduceComputed tries to skip walking all observer contexts when an item
property changes if the current tracked array state is [retain:n]. However,
this check occurs while applying the operations. If [delete:m retain:(n-m)]
is applied, when the retain operation is visisted it will have been updated to
retain:n.

This commit updates the check so that retain:n is only checked for the *first*
operation.