Steps to Reproduce

1. run <textbox onChange=""/>
2. enter $z!t#d: in the textbox

Current Result

zk.wpd:28808 POST https://temp.zkfiddle.org:8080/t9512sp/zkau 400 (Invalid Request (see: Server logs for details))
ajaxSendNow @ zk.wpd:28808
sendNow @ zk.wpd:29431
(anonymous) @ zk.wpd:28779
setTimeout (async)
ajaxSend2 @ zk.wpd:28779
ajaxSend @ zk.wpd:28773
send @ zk.wpd:29077
sendAU_ @ zk.wpd:24280
fireX @ zk.wpd:24224
fire @ zk.wpd:24319
updateChange_ @ zul.inp.wpd:782
doBlur_ @ zul.inp.wpd:489
(anonymous) @ zk.wpd:20503
dispatch @ zk.wpd:5614
elemData.handle @ zk.wpd:5418

Expected Result

no error

Debug Information

https://github.com/zkoss/zk/blob/v9.5.1.2/zk/src/org/zkoss/zk/au/AuRequest.java#L102