Mining netherrack with effciency iv sometimes creates invicible block

Hi. i was recently playing minecraft and started to clear out a tunnel in the nether, as i was mining with a diamond pick with effciency iv. i got stuck in an invicible block and was not able to move, i threw an enderpearl to get out of the block. i placed a quartz block on the invicible block and it turned into netherrack. i mined the netherrack and it was fine. this happened many times making the tunnel. i hope you fix it! Keep up the good work! liking 1.9 alot so far!