summon armor stand with fractional x or z coords puts it in the wrong location

If you do:

summon minecraft:armor_stand 77 57 147

it appears in the middle of a block. All fine. But if you do:

summon minecraft:armor_stand 77.2 57 147 

Even though the X value is higher (.2 instead of 0), it appears farther west (negative x) than the first armor stand.