BFP on expired pregnancy test kit

I'm 6 days late for AF, but didn't think I could be pregnant as I've had a period since the last baby dance and we haven't tried this month. 
​But, being late, I thought i'd use up an out of date pregnancy test left over from my first baby (the test expired in Nov 2012). And it's come back positive.
​ 
​So confused! Google tells me that you're more likely to get a false negative from an expired test and that it's usually the dye in the test tht expires.
​It's a public holiday today, so no shops are open to buy a new test until tomorrow.
​Has anyone here had experience of results after expired tests?!