Is this a RegExp bug??? Matching double letters inside words...

I'm trying to match double letters inside words, excluding ones that begin or end a word.  I'm running into a problem matching \B at the end of a line.

example:

My RegExp is /\Bdd\B/gi

String is "dda adda add add"

This will match twice, the dd in the 2nd word, and the dd in the 4th word.  Why is it matching the 4th word??