Thanks Ross,
Generally speaking (although not as an absolute rule - context is always key), I'd suggest that these are normally not materially significant the the outcome - i.e. the record/document that is ultimately produced, therefore the presence of a *.tmp file that identifies as a Word Document, combined with the fact of an extension mismatch, is more of a research trigger: Why do we have these? Do we want them? Is there an associated file that is ultimately the canonical record?
So my feeling is that .tmp is generally not a useful extension as far as PRONOM is concerned, rather its absence as an extension is more useful from a data/record curation perspective.
Alternative perspectives gratefully received...
David