Interesting. I just looked it up and you are right, that is what the Technical Explanation says.
If a professor or teacher remains in the host State for more than the specified two-year
period, he may be subject to tax in that State, under its law, for the entire period of his presence.
<a rel="nofollow" target="_blank" href="
https://www.irs.gov/pub/irs-trty/inditech.pdf#page=50">https://www.irs.gov/pub/irs-trty/inditech.pdf...>
