I have seen something odd as well. Placing a Takistani BMP2 and a US Stryker head to head, the BMP2 doesn't engage. The Stryker also won't do anything either, unless it's a TOW or MGS version. The BMP also won't engage a M1A1.
This is weird as hell because the gun on the BMP2 can kill a Stryker no sweat and it's rockets are also fairly effective, even against an M1.