Are you entering a blank line between the numbered sections? for instance:
1) numbered sentence one
2) numbered sentence two
3) numbered sentence three
A sentence on a separate line goes here.
1) A new line numbered sentence one
2) New line numbered sentence two
If so, then that is Words normal operation. It can be fixed for selected text areas by going to: Format/Bullets and numbering/ and then selecting "continue from"...
but nothing that I know of will cause it to just automatically keep counting up.