Hi Filipe,

Recently I also had this problem for currency mask. My solution was to make the input KeepMask = True and use this on AdvanceOptions {autoUnmask:true}. So to fix your problem you would need to change the MaskDate and include a input KeepMask and on the js wrap the below code with a if like this "if (keepMask == "False") {"

SyntaxEditor Code Snippet

    var Base_OsPage_ClientValidate = OsPage_ClientValidate;
    OsPage_ClientValidate = (function (srcElement, cleanOnlySrcElementErrors) {
        $(elementID).inputmask('remove');
        var result = Base_OsPage_ClientValidate(srcElement, cleanOnlySrcElementErrors);
        $(elementID).inputmask(dateFormat, maskOpts);
        return result;
    });

    osAjaxBackend.BindBeforeSubmit(function () {
        $(elementID).inputmask('remove');
    });
    osAjaxBackend.BindAfterSubmit(function () {
        $(elementID).inputmask('remove');
        $(elementID).inputmask(dateFormat, maskOpts);
    });

Hope this helps,

Regards,

Marcelo