Unfortunately it looks like we’ll need some further details on how to see either of these problems. I have never seen tables break apart when adding paragraph breaks within a cell, and for me, what formatting exists in the table (cell background color and border settings) are applied to new rows and columns, no matter how they are added.
I’d also do some checking in TextEdit. If you copy and paste the section of text containing the problematic over into a new TextEdit window and do some testing there, do the problems persist? If so it’s not very likely there is anything we can do about it.