It is nice to thank someone who praises you.
Jack and his boss are in a meeting and Jack's boss thanks Jack for a job well done.
Jack wants to not appear awkward in front of his boss.
Jack thanks his boss for the praise before continuing on with the meeting.
Jack says nothing about the praise and continues with the meeting.
Jack's boss is pleased.
Jack's boss may think Jack is being rude or did not appreciate the praise.