Failed to "Change Owner" when select batch operation in "Calendar List/Action"

Hi everyone,

I'm now facing an issue: When I get to “Calendar List” and select multi-rows and then click "Action/Change Owner”, all the contents of the calendar items are removed and only the owner names are kept if I click "Save".

The screen-shot is attached and the first row marked is for troubleshooting.

Not sure if it is a patch. If so, hope there is patch to fix it.

Vtiger version: 6.5.0

Thanks.