Nope, just working my way down from cover page file to the bottom of the last page file with setting "all text files". It just happened to me today again on removing superfluous </span>'s. With big changes I always check. On this occasion I expected to see just 1 intentional </span> left in a previous chapter, but that was gone
So I decided to mention it here for the benefit of others.
I know that Edit-Book behaves differently than Sigil, but expected somehow similar behavior for F/R "downwards".
For the good order: I am now capable to do my touching-ups completely in Edit Book; no need to use Sigil anymore. That is a great plus (as always: thanks Kovid!)