I realise this topic has been covered in another thread, but my experience is slightly different, and i thought it worth posting because I suspect many others will discover this the hard way.
I was forced to upgrade from 0.7.1 to 0.7.4 because I had installed Maverick 10.9.1 on my MacBook. I immediately found that making any edits in Book View caused to be replaced initially by
Code:
$#160; where $ is &
and later to just a space. As I had rather lazily used the construct <p height="40"> </p> to achieve a certain size spacing, this was eventually rendered useless.
I took the advice given in the other thread to add to my css so that I could create the spaces I needed by adding a class to those elements where a space was needed either above, or below. So I am no longer bothered that this behaviour occurs, although I did have to put in a few hours to recode over 20,000 lines. But I feel sorry for any folks creating books in French.
I have found Sigil a very useful tool, and so I am glad I have a work around.
thanks
Geoff