Well, that IS curious. Not only the RSV, but the ASV also has the translation of Καὶ ἔρχεται εἰς οἶκον moved into verse 19. I was thinking, "The ASV is older, perhaps it'll give us a clue." So, I checked Westcott and Hort and Tregelles (the two texts that the ASV is mainly based on) thinking that an older translation might help indicate why the different placement. Nope, both W&H and Tregelles have the clause in verse 20. So, the versification of the underlying text has it one way, but the versification of the translated text places it differently! The whole way back to the ASV.

Perhaps older?

Turns out it's Textus Receptus. So, as Tevye would say, "Tradition!"

See: textusreceptusbibles.com/Interlinear/41003019. You might need to put Mark 3:19 in the drop-downs. But, you should see that the Greek clause is positioned at the end of verse 19.

Is there a "curious question" badge? :-)

Well, that IS curious. Not only the RSV, but the ASV also has the translation of Καὶ ἔρχεται εἰς οἶκον moved into verse 19. I was thinking, "The ASV is older, perhaps it'll give us a clue." So, I checked Westcott and Hort and Tregelles (the two texts that the ASV is mainly based on) thinking that an older translation might help indicate why the different placement. Nope, both W&H and Tregelles have the clause in verse 20. So, the versification of the underlying text has it one way, but the versification of the translated text places it differently! The whole way back to the ASV.

Perhaps older?

Turns out it's Textus Receptus. So, as Tevye would say, "Tradition!" [Edit: So, I think the answer to your question is that the discrepancy is caused by the translator's attempt to help Teachers navigate the change over time in the versification of the underlying Greek text.]

See: textusreceptusbibles.com/Interlinear/41003019. You might need to put Mark 3:19 in the drop-downs. But, you should see that the Greek clause is positioned at the end of verse 19.

Is there a "curious question" badge? :-)