automatic player position switching *player naming*

im currently going in to a new season with my arsenal team in 2013

during my pre-season tour of Brazil I came across a problem with my teams,

about 20 mins in to my match against Vasco, my right-back (Bakary Sagna) was up-front, and my striker (Adebayor) was at right-back

i swapped them back and everything was fine

then it happened 3 more times, even after i had subbed them

anyone know why they keep doing this?

and before anyone says it, no there player instructions aren't set to swap positions