Thank you for reproduce this issue for me!
I found out what was wrong,i added a method to javascrip to custom validate(high light textbox when error)
function ValidatorUpdateDisplay(val){....}
this is link refer :http://blogs.msdn.com/b/valdon/archive/2010/02/11/customizing-asp-net-validators-without-using-the-customvalidator-control.aspx
if i remove this function,it's working well.
So,i have a question is how i detect this page is CMS desk page or Live page in JavaScript
to i'll modify function
ValidatorUpdateDisplayfunction ValidatorUpdateDisplay(val){
if(!isCMSDesk)
{....}
}
ps:function
ValidatorUpdateDisplay in file .js so CMSContext.ViewMode is unusable
thank and best-regards!
Giang