Comparing Göttingen Isaiah and Rahlfs, I get several words highlighted (and listed in the text differences section) that appear to actually be identical:
τῷ ἐμῷ λαῷ in 10:6, for example.
Nothing on the surface text--not even surrounding punctuation, which is highlighted differently anyway--indicates any difference. The parsing info in Instant Details for ἐμῷ is ever-so-slightly different, however.
ἐμῷ ἐμός (ἐγώ) Adjective masc sing dat (poss) my
ἐμῷ ἐμός (ἐγώ) Adjective masc sing dat noDeg (poss) my
Is this parsing info enough to trigger the highlight? My preferences for Compare Text are set at "Words," not "Tags," so I'm unclear as to why I get this result--and there are other examples of the same, too, not just at 10:6.