Passwords are lost when editing the protected node

I got the following problem:

When I protect a node by giving a password (check the checkbox and fill in the password twice and save afterwards), everything seems to be okay. But if I am editing a protected node, the passwords will not show up in their fields of the edit-form. The checkboxes are displayed correctly. They passwords seem to be saved correctly (protection works), but are not filled in in the edit form.

This leads to the problem that you have to reenter the two passwords everytime you are editing the page.