need help for formating timestamp on round trip: db -> browser -> db

I have a date in the sqlite3 database which gives me trouble

select * from accounts;

3|myname|2011-07-10 13:47:26.055000|2011-07-10 13:47:26.055000

putting it into html via the hidden_field.tag like this

    <%= f.hidden_field :updated_at %>

here f comes from

    <%= form_for(@account) do |f| %>

that produces working html code as such

    <input id="account_updated_at" name="account[updated_at]" type="hidden" value="2011-07-10 13:47:26.055000" />

now I need to add the very some date as query parameter to an url of a link and following code works most of the time but NOT with that example from the database:

<%= link_to 'Destroy', account_path(account) + "? account[updated_at]=#{account.updated_at.utc.strftime('%Y-%m-%d %H:%M: %S.%N')}", :confirm => 'Are you sure?', :method => :delete %>

which produces

<a href="/accounts/3?account[updated_at]=2011-07-10 13:47:26.550" data- confirm="Are you sure?" data-method="delete" rel="nofollow">Destroy</

this query-parameter parses into a different date then the one I have in the database - so I can not find the model in the database.

background is an optimistic persistence with the help of this timestamp since I like to keep the model slim and the activerecord default would add another "version" column to it.

bug ? or how does this hidden_field method does it right ? I was not able to find the right spot in the code.

thanx in advance. Kristian