problem nesting enumerate lists

[Piersante Sestini]

I have a problem formatting enumerated lists in a document.
What I need is
==
1 item bla bla bla bla
    (a) sub-item
    (b)another sub-item
  continue item 1 again bla bla bla

2 another item bla bla bla

However, what I get is:

1 item bla bla bla bla
    (a) sub-item
    (b)another sub-item
2  continue item 1 again bla bla bla <---!!!

3 another item bla bla bla

==
How do I prevent lyx from inserting a new item number after the last 
sub-item of a list?

thanks,
Piersante