From my experience writing official documentation for a C library, another possibility is that the exact circumstances under which the files are removed from memory are more complex than anybody wanted to explain.
There is always a push to KISS. Judicious use of the word "typically" us often the compromise between giving the full story and saying something untrue. "Typically, when you XXX from XXX the XXX will be deleted and replaced with the XXX from XXX".
Ideally we would have enough information in play for the user to take an educated guess at the true ruleset, but it's hard to tell your editor "I included this sentence so that the reader can solve an exciting puzzle in search of deeper knowledge!"
Biting the hand that feeds IT
