Problem with Active Record find

Hi all,
I migrated my Rail version from 1.2.3 to 2.2.2
I got one problem while going around.
User.find(params[:id]) some times its returning Array and some times
its returing User record.

If I see the log, some times its
select * from users where (‘users’.id in (1))

and some times its
select * from users where (‘users’.id = 1)

Why is this happening?
And that also it returns Array when I run the include queries and run
the general record User.find(params[:id])

Did any one faced this??
My Ruby version is ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]
Rails version is Rails 2.2.2

Is there any problem with the versions?