Recently a feature was added to make certain mobs try to quickly get out of the blast radius when a creeper near them is about to explode. However if there are 2 creepers and the one that is further back is about to explode it can make the nearer one RUN straight at the player! It's like crossing the creeper with the baby zombie!

When it happened to me it was with 2 creepers walking almost side by side but one was one eighth of a meter further back, so either one would react at pretty much the same distance. When I moved within range the further back one reacted first, so the more forward one ran straight for me. This could also happen with a sprint-attack that threw a creeper back behind another.