Presented in illustrations:

; dig +short ns harvest.idv.tw.
harvest.idv.tw.
www.harvest.idv.tw.
; dig +short a harvest.idv.tw.
219.84.30.59
; dig +short a www.harvest.idv.tw.
219.84.30.59

To those setting up nameservers: when people said 'have two nameservers', they did not mean 'and feel free to give them the same IP address'.

As a bonus, harvest.idv.tw has probably doubled the amount of time many DNS servers take to give up on them when 219.84.30.59 is having a wee problem.