Passing variables via input/onclick

Here I am again!

I need to pass three fields via input/onclick.  The first is a constant, and the next two string variables.  I have to use input because the user wants a button to push.  This is a bummer because <a href works great.  It's that darn button!

Here's the code:

<input type="button" name="addnew" value="Add New Leave Request"

     onclick="location.href='index.cfm?fuseaction=add_new_leave&leave_id=A&user_id=#UserID#&user_name=#UserName#'">

I get to index.cfm, and to the correct fuse action.  But when I perform a dump of the URL at this point, all I get is:

leave_id           A

user_id            [empty string]

fuseaction        add_new_leave

No mention of user_name at all.  CFOUTPUT statements before the input statement indicate that UserID and UserName have valid values.  I figure the problem has to be with the way I am formatting the onclick clause, but just can't figure out what the problem is.

Any suggestions?