Do you work with the Nonprinting Characters visible?
There are probably multiple superfluous Paragraph Marks, Tabs, etc. which
can be causing your problems.
Use Ctrl+Shft+8 or the ¶ icon (on the Home ribbon or the Standard toolbar)
to toggle the view of these.
See: http://www.word.mvps.org/FAQs/Formatting/NonPrintChars.htm for further
details on these very useful little blighters.
Also you may have other Paragraph settings such as Keep with Next, Keep
Lines Together and Page Break Before applied though out the document. When
Showing the nonprinting characters you may see a small black box appear in
the left margin, this indicates that that paragraph (or somewhere within that
line) has a such a Paragraph setting applied. You can also use Find to search
for these settings.

Come back if your problems still persist.
Hope this helps
DeanH