The difference in the ID is introduced in both rendering modes currently available for RadInput. There is no setting or property for allowing old style rendering and you would need to change all pieces of code that look for an ID having "_text" in it. You can take a look at this blog post to see all the changes in RadInput introduced in Q2 2012.
Changes in RadInput in Q2 2012 version of RadControls
At the bottom of the post you can see the changes you should do to get everything working properly.
the Telerik team
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