Proverbs 26.11
Septuagint

wster kuwn otan epelqh epi ton eautou emeton kai mishtoV genhtai, outwV afrwn th eautou kakia anastereyaV epi thn eautou amartian

New Testament - 2 Peter 2.22

kuwn epistreyaV epi to idion exerama, kai:  uV lousamenh eiV kulismon borborou
 

Septuagint

As when a dog goes to his own vomit, and becomes abominable, so is a fool who returns in his wickedness to his own sin

New Testament

The dog turning to his own vomit again, and the sow that had washed to wallowing in the mire
 

Masoretic Text

As a dog that returneth to his vomit, So is a fool that repeateth his folly

Comments:  The NT, LXX and MT agree.  Clearly, not a careful quotation from the LXX.