Reversal of currents

http://www.physics.ox.ac.uk/olympiad/PastPapers.html#BPhOP2
for the 2010 paper 2, question 5bi, i dont understand why i2 would equal i6 and not i5? please help

Looks like an error in the answer sheet. If the voltage is reversed and all of the resistances are equal, then it follows that all of the currents except i₄ would reverse but all of them would stay the same magnitude as the original.

i.e.

i₁ becomes -i₁
i₂ becomes -i₂ etc.

i₄ stays i₄