Height...
I am thinking it is because of the compression of the cartiledge in your knees and spine. All the extra weight squishes everything together so when you take the weight off it doesn't squish anymore. Well at least this is what my moms guess is. She is a nurse so I will take her best guess!! LOL
I am kinda liking the extra inch and a half. Especially since the guy I am seeing is 6'5" LOL. Even with the extra height I can still wear 4 inch heels and have to look up to kiss him! It's GREAT!!