is this a one-off flucuatuion or the start of a trend?
Actually, it's not PO that you should be looking at, but rather that PiS has dropped to 22%. That's a clear sign that they're failing in opposition - and probably also a sign that Ziobro did indeed snatch a portion of their electorate.
I do think it's quite likely that we'll see some complicated electoral possibilities in 2015 - so yes, it could be a sign that things are about to get interesting.
But - as always - PiS are nowhere to be seen. 22% won't win them an election!