Contact forms wiht the sam form id

When i create a new form an already existing form-id is used
f.e.
new form created: [contact-form-7 id=”2322″ title=”test”]
existing form: [contact-form-7 id=”2322″ title=”Register Event 1″]

When i save the new form , the old form is overwritten.

is there any way to change the form id, or find out the root cause why the same form id is used twice?

thanks
Brigitte