Summoning a Mannequin with a macro specifying its model type ignores the macro and uses a random one

When summoning a Mannequin within a function that has a macro passed in with the model type the Mannequin should have it ignores the model specified of the macro and uses a random model type instead:

# Macro:
# $(model_type) --> Its model type (wide or slim)

# Summon:
$summon minecraft:mannequin ~ ~ ~ {model:'$(model_type)'}

# Output for slim: summon minecraft:mannequin ~ ~ ~ {model:'slim'}

Even tho the macro specified the “slim“ model type it will be ignored and a random model type will be used instead.
I actually created this bug report because I was trying to summon a slim Mannequin but it was summoning a wide one everytime but when I went and recorded some proof then it only summoned slim ones, so I suppose that it is random (tbh, when it was only summoning wide ones there were a few other macros for its name and skin texture, so that may be related to this).