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

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

sqlite> 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

Destroy</
a>

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