validationMessage binding displays stale error message if property has multiple validators attached

[xelibrion]

Please have a look at the fiddle http://jsfiddle.net/twgwM/14/

After clicking "Current month" button against the second input the message will say "This field is required", although it should say "End date must not exceed current date".
In fact, the error property of observable has exactly this message (you can see it in console after clicking on 'Validate' button), but it looks like for some reason validation message was rendered before it had been actually set.

[crissdev]

Fixed by #248