Right! That's the RAW, but it basically makes countering a non-option, IMO, which I'm never a big fan of.
I think if this came up IMG I'd allow a Spellcraft check before entering the darkness effect to determine the center of the effect, then allow the caster to successfully counter the darkness spell if they cast their light spell on the appropriate vertex/square...at Touch range, of course.
Would anyone do it any differently? And if so, how & why?