Nibbaanasukha sutta

Dear Pali friends,

In the Nibbaanasukha sutta

http://www.accesstoinsight.org/canon/anguttara/an09-034.html
http://www.tipitaka.org/tipitaka/s0404m2/s0404m2-31.html

in the description of fourth jhana there is
a passage:

tassa ce, aavuso, bhikkhuno iminaa vihaarena viharato
upekkhaasahagataa sa~n~naamanasikaaraa samudaacaranti, svassa hoti
aabaadho.

which is a bit strange since rather 'sukha' is a hindrance in fourth
jhana instead of 'upekkha'.

Could it be that an error has crept in? Or something special is meant?

Metta,
Dimitry