[Samba] Do Machine Accounts Expire?

[lists at trcintl.com]

I recently started playing with pdbedit to set the maximum password age policy on v3.0.25a.  After setting 
this policy, I see that running pdbedit -Lv shows the machine accounts expiring in the same time frame as 
the user accounts.  So my question is do the machine accounts actually expire just like user accounts?  If 
they do, is there any way to set the machine accounts not to expire as a group instead of setting them not 
to expire one at a time?

Thank you in advance.