Your blog posts on February 18, 2010, and January 12, 2011, (accessible by typing "sabbatical" in your search window) offer the only specific statements along these lines that I can find, anywhere. I would like to have as much authority behind me as possible. Can you please refer me to something from IRS or others that provide the authority for your statements?
Both blog postings reference IRS Publication 463. Chapter 1 of the 2010 edition offers on only 6-7 pages of content a good initial read. Chapter 6 includes roughly 4 pages on reimbursements under Accountable and Nonaccountable Plan rules.
The Publication defines travel expenses that qualify and offers extensive examples. Further, its section on accountable plan rules offers direction to churches wishing to set up arrangements that establish reasonable reimbursement plans.
Here's a link to the Publication in .pdf format:
IRS Publication 463