max-date doesn't work with future dates

specifying max-date:-1y works fine i.e. only allowing dates up til one year ago.

But specifying future dates doesn’t restrict the picker
e.g. max-date:+1y or even max-date:365 (i.e. 365 days) instead there is no restriction

Otherwise, a great easy to use plugin

http://wordpress.org/extend/plugins/contact-form-7-datepicker/