Some tax treaties, such as the one between the US and Germany, have different articles for professors/teachers/researchers and recipients of scholarships. In the aforementioned case, these are articles 20(1) and 20(3), with some mutual exclusions. In the 2006 version, these read:
Article 20 (Visiting Professors and Teachers; Students and Trainees)
1. Remuneration that a professor or teacher who is a resident of a Contracting State and who is temporarily present in the other Contracting State for the primary purpose of carrying out advanced study or research or for teaching at an accredited university or other recognized educational institution, or an institution engaged in research for the public benefit, receives for such work shall be taxable only in the first-mentioned Contracting State for a period not exceeding two years from the date of his arrival. This Article shall not apply to income from research if such research is undertaken not in the public interest but primarily for the private benefit of a specific person or persons. The benefits provided in this paragraph shall not be granted to an individual who, during the immediately preceding period, enjoyed the benefits of paragraph 2, 3, or 4.
3. Payment other than compensation for personal services that a person who is or was immediately before visiting a Contracting State a resident of the other Contracting State receives as a grant, allowance, or award from a non-profit religious, charitable, scientific, literary, or educational private organization or a comparable public institution shall not be taxed in the first-mentioned State.
So when receiving a scholarship as a professor, teacher or researcher, both articles may apply. Can one choose to claim an exemption under (1) even if (3) is applicable? If not, this would mean one could lose the possibility of claiming an exemption for future remuneration which is not a scholarship.
Follow-up question: can one choose not to claim tax-treaty benefits for some income (for example, said scholarship) in order to avoid losing later benefits for teacher remuneration?