execute as @a at @s in the_nether if entity @a[distance=0] run say nether

correctly executes for each player in the nether but not for players in other dimensions.

execute as @a at @s in the_nether if entity @s[distance=0] run say nether

executes for all players regardless of dimension.

The distance check for @s appears to use the dimension of @s instead of the dimension where the command is being executed to calculate the distance to @s, thus making the if entity clause always true.

This also occurs when using positioned x y z or no positioning instead of at @s.