change Drop Down(single select) field value problem

Hello
I use joomla 2.5.26 and cb 1.9
I have about 200 students profiles in my site
there is Drop Down(single select) field called teatcher
teatcher field has values (teacher names) like John , Adams ,.....
every student profile has one of this teachers names

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My problem is :
I change the value of teacher Drop Down(single select) field from John to John1 from fields manager ,but all students who has teacher field value=John in profile still John in database and not changed to John1
so,I need to enter every student profile who has John value and select John1.
I think this is bug.
can someone help my to solve this problem .
thanks

Hi

I would like to know some clarification on this.
IMHO, Drop Down (Single Select) values should be stored as integers, so that value Title could be changed if needed.
There are many many times when something needs to be changed after initial setup.

Regards