AJAX async postback is behaving differently... ?

Question

Hi All,

We have implemented the Ajax (using scriptmanager, updatepanel) for one page and it has functionality like if I click on checkbox it should display the textbox. We have deployed the same to QA machine and when trying to use QA url and test the functionality its working as expected. But same code has been deployed into UAT and found different behavior. Here is diff both QA and UAT

QA:

If click on Check box then its hang up some time to execute the server side code and responded. 

UAT:

If click on Check box then it's not hang up  and use can enter any value on any control and once response done what ever i entered in other control data will be cleared.

IS ajax will behave differently based on browsers or environments.

Any ideas.. Please share...