Purchase some antennas from a reputable manufacturer such as VAS and I'm willing to bet you will find a world of difference in the way they perform and isolate from RHCP to LHCP.
Everybody loves a bunny.
Axial ratio has been discussed earlier, so I'll just explain environment:
To 5.8GHz, every solid surface is a reflector. It is like a world of mirrors to light. Thus, the signal can bounce (effectively reversing propagation) and thus be received by the opposite rotation antenna. Mind you that how well the signal is received depends highly on axial ratio and where you happen to be flying. This is therefore highly subjective and difficult to understand as simply changing where you are standing might yield completely different results.
If it is broken, fix it. if it isn't broken, I'll soon fix that.
videoaerialsystems.com - Performance video piloting