Got this alert earlier:
Park St: Beginning Wed, Apr 30, the D & E branches will switch berths with D branch trains berthing on Track 2 & E branch trains berthing on Track 1
Green Line D branch
Green Line E branch
Last updated: Apr 25 2014 3:58 PM
As to why this is sensible - at present D trains terminate at Park Street most of the time due to Government Center being closed, and this change will eliminate the "musical platforms" nonsense that currently happens.