that sounds like a 2 way using the single as the common strapper ,its sounds as though the wires are crossed , this is a prob to sort out when all the colours are the same and which 2 way wiring is used so , first you need to find out which is the supply switch off power and put each wire into a terminal block seperatly do this at each end where the 2 ways are , switch power back on and test to see which is live , once you have found the live connect that to the comon terminal of the light switch and connect the other 2 wires to L1 and L2 , then go to the other terminal block for the other switch and test to see which is live , when you find a live wire connect this to L1 of that switch ,go back to the first switch and then switch it on , go to the 2 switch you should have 2 wires in the terminal block test these and find which ones live , when you find it connect this to L2 , you should then be left with one wire which tests as dead , connect this to the common of the 2nd light switch and that should reinstate the 2 way , that is if it is a 2 way switching using the method ive described
hope this helps