How do you set a form's custom success message?

[dealio]

I set in forms processing options:

success message = Your Message Has Been Sent.
suppress message = Ive tried of the options


I've cleared cache, and still the default message shows.
Message

Record added/updated

 

[troester]

A custom success message is working on my site, "supress message" options seem to be ignored (no differece which is selected).
Do you have form plugins (redirect)?