Double the size

The following code snippet shows a size of 10, but #do: processes  
those 10 items twice. Any ideas what I'm doing wrong?

m := MagmaCollection new.
1 to: 10 do: [:each | m add: each].
Transcript show: String cr, 'size: ', m size asString, String cr.
m do: [:each | Transcript show: each asString, String cr].

Brian.