question for STP

You mentioned before that US-China treaty does not apply if you transfer from other visas instead of getting H-1 or J-1 directly from China. I called IRS today, and talked with three associates (for one and half hours). They told me that for China, it is ok if you transfer from other non-resident visa such as F-1 as long as you have not claimed as a researcher/teacher/lecturer under the tax treaty before. I want to know where you get the information that transferred visa is not ok? Can you provide a link?

Thank you very much.