Players in spectator mode are detected when using the /testfor and /execute if entity commands

Steps to reproduce: 

1-type the command /testfor @a[x=~,  y=~+1,  z=~,  dy=2] or /execute if entity @a[x=~,  y=~+1,  z=~,  dy=2] in a command block.

2- place a redstone comparator next to the command block.

3-stand on top of the command block

Observed results:

the command block will detect all players in any game mode.

Expected results:

players in spectator mode were not supposed to be detected by the command block, as players in spectator mode were not supposed to interact in the game, just observe.