LUD changed 3 times after RFE received.
In my case also LUD changed on 12th(RFE RD), 14th and 15th.
In two of my friends cases LUD changed only two times then they got approval exactly after two weeks they submitted RFE response. I think whenever they do something on the case LUD changes which is good at least to know something is going on.
I140/I-485 Concurrent filing - Oct. 2003
I-140 AD - March. 2005
I-485 RFE (for EVL) - 03/31/05
I-485 RFE RD - 04/12/05 (self)
LUD change - 04/12/05 (RFE response received), 04/14/05, 04/15/05
I-485 AD - ????