Parameter :requirements in routing doesn't use implicit anchors

Consider the following route:
map.detail "subscription_plans/:provider/:plan", :action =>
"detail", :requirements => {:plan => /[^ ]+/}

I want this route to match any string without a space character. So
"Telfort-100" matches "Telfort 100" does not. This however does not work. It matches both.

I believed this to be correct but it's not. Including anchors ('\A'
'$' etc) is not allowed and the docs seem to suggest they are implicit.