Although the last example is clearly a bug, is there some difference in behavior between HoldComplete and Hold that generally accounts for these issues? The documentation mentions differences with respect to Sequence, Unevaluated, Evaluate, and upvalues. Without knowing the internals of the expression manipulation functions, I fail to see how any of these are relevant here.
(1) FactorTerms behaves incorrectly if the independent form is more complex than a symbol and not contained in the expression. Example:
In: FactorTerms[x, x^2] Out: Sqrt[x]
In my understanding, FactorTerms should always return an equivalent expression. Is this a bug or some sort of undocumented behavior? Does FactorTerms require the independent form to be a symbol?