Boh-kai Lek!!! (or is it Diak Diak Lu?)

All his life, Daryl has been thanking his Hainanese family and relatives with the familiar "Boh-kai Lek" which means thank-you in Hainanese. That's what he's been using, that's what he's taught his wife and even his children. Recently, his in-laws went to Hai Nan Dao (Hainan Island) and learned to say 'thank-you' as "Diak Diak Lu". They learned that "Boh-kai Lek" is the greeting after "Diak Diak Lu". You know, like how we say in Mandarin "bu ke qi" after someone thanks us with a "xie xie". That baffled Daryl and his parents are in disbelief. Can anyone give us the truth?