This has never really bothered my until now when I've tried doing more advanced stuff. If I play a low note and let it ring, e.g. I just play an open E string, and then try and play a higher note, such as the B string, the E string will continue to resonate but the B won't come through until I mute the E string

They're EMG-HZ stock pickups, but I don't know much about pickups so can someone help me out? Is this just how guitars work, something to do with dominating frequencies or something, or are my pickups just crap?