In het post form of the collaboration system these two form helper template variables are used:
                    tmpl_var stick.label
                    tmpl_var sticky.form

They do not produce any output if you edit the thread. Effectively making it impossible to ever change the sticky status.

In the default templates they can be found within the tmpl_if isNewThread tags. This is why this bug doesn't hit the eye instantly.

See this beta demo  or this stable demo both with standard login.

Kind regards,

Arjan.