Constraints doesn't work in workflows

I'm making an advanced workflow in which there is a simple task with one field to fill. I put a constraint on it. At the beginning I was thinking that I did something wrong, because I was able to put whatever I wanted. But I find out that if I press the "Save Change" button I have the wanted message (warning about the incorrect input).

So is there a way to have the constraint check before the workflow goes to the next step ?

I've never tried to use the types of LENGTH or REGEX. Maybe you could try to use the type "text" in an additional constraint or by changing an existing type - through it you could find, if it's a problem with your configuration (problem persists) or with the special types of constraints you're using.