When doing an action such as running debuild for package signing, seahorse will pop-up a dialog to ask to unlock a GPG key if it has a password (but is not yet recorded in seahorse for whatever reason).

seahorse uses a modal dialog for this request, which prevents the user from using another password management application such as Keepass to copy+paste the password into the dialog.

It is not clear that a simple modal dialog is actually providing any enhanced security in this case (the dialog went unmodal on one invocation for unclear reasons), and there is no way to disable this functionality in seahorse itself.