[Rails] Rails 3.07 dup issue

Hi not sure if this is where I should post this problem but since
upgrading to rails 3.07 dup is not working as expected for Hash

basically in method I have this
dup_row = row.dup
#then I delete a row of my original hash
row[:athlete].delete(:sports) if !row[:athlete][:sports].nil?

pretty simple but what is happening is it is deleting from the dup
and the original here is the debug
code of the original and dup just after deleting the sports

original hash values

{"athlete"=>{"first_name"=>"DaveG5600", "gender"=>"M",
"hometown_id"=>"40", "birthplace_id"=>"30", "last_name"=>"test"},
"leagues"=>{"league"=>{"id"=>"821", "start_year"=>"1983",
"end_year"=>"2003"}}, "clubs"=>{"club"=>[{"id"=>"11802",
"start_year"=>nil, "end_year"=>nil}, {"id"=>"1403", "start_year"=>nil,
"end_year"=>nil}]}, "schools"=>{"school"=>{"id"=>nil,
"start_year"=>nil, "end_year"=>nil}},
"sports"=>{"sport"=>{"id"=>"102", "start_year"=>"1985",
"end_year"=>"1986", "sport_roles"=>"10"}}}}

dup row (notice sports is missing which even though I am not deleting
from this hash)
{"athlete"=>{"first_name"=>"DaveG5600", "gender"=>"M",
"hometown_id"=>"40", "birthplace_id"=>"30", "last_name"=>"test"},
"leagues"=>{"league"=>{"id"=>"821", "start_year"=>"1983",
"end_year"=>"2003"}}, "clubs"=>{"club"=>[{"id"=>"11802",
"start_year"=>nil, "end_year"=>nil}, {"id"=>"1403", "start_year"=>nil,
"end_year"=>nil}]}, "schools"=>{"school"=>{"id"=>nil,
"start_year"=>nil, "end_year"=>nil}}}}

row (this is where I expect to have the sport value deleted which is
does)
{"athlete"=>{"first_name"=>"DaveG5600", "gender"=>"M",
"hometown_id"=>"40", "birthplace_id"=>"30", "last_name"=>"test"},
"leagues"=>{"league"=>{"id"=>"821", "start_year"=>"1983",
"end_year"=>"2003"}}, "clubs"=>{"club"=>[{"id"=>"11802",
"start_year"=>nil, "end_year"=>nil}, {"id"=>"1403", "start_year"=>nil,
"end_year"=>nil}]}, "schools"=>{"school"=>{"id"=>nil,
"start_year"=>nil, "end_year"=>nil}}}}

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