[otrs] Agent can not select a customer using "Customer User"Management when create new ticket

Hi,list I noticed a weird issue in OTRS3.3.7. When signed in as agent with RW Admin rights, I am able to click the "Customer User" link next to Options and pick a customer using the Customer User Management window. However, when signed in as a agent with RO Admin rights,the window comes up without "Customer User"link. How the agent without RW admin rights can use the "Customer User" link in create new ticket windows? Thanks very much!