LyX ⇒ Problem with front/back

[Elettrotanzboy]

Hi,
I write to you as I am quite desperate: I wrote all my master thesis in LyX using the memoir class. After, I realized that I had not activated the front / back: the problem is that activating it now leaves huge spaces between one voice and another of a bulleted list or when I go to point and head.
Can you tell me the reason for this behavior?