When you select find-in all buffers in mini find a few problems:
The find box is red if the current buffer doesn't match.
hit F3 and it will move on to a buffer where there is a match.
The find box stays red however.
Toggling case-sensitive doesn't work reliably once you have done Find-Next into the next buffer.
Sometimes I found that toggling case sensitive did nothing.
Sometimes I found that when I edited the find text box (changing a letter from lower to upper), hitting F3, and the text box would revert back to the all lower case text. (Possibly this is interference from search options->InializeSearchString with selected text).
Shift-F3 sometimes would restrict itself to the current buffer, but not always.
F3/Shift-F3 do not seem to follow the same order of buffers -- I'd expect Shift-F3 to go exactly in reverse of F3, but it doesn't.
Shift-F3 doesn't notice changes to color-coding options unless you F3 first.