type family creates a type synonym, which should not be created

Summary

We can use types that never allowed (example below)

Steps to reproduce

λ> :set -XTypeFamilies -XMultiParamTypeClasses -XFlexibleInstances -XUndecidableInstances 
λ> :{
class HasX a where
  type X a
instance Eq a => HasX a where
  type X a = a
:}
λ> :kind! X (IO Int)
X (IO Int) :: *
= IO Int
λ> z :: X (IO String) ; z = getLine
λ> z
1
"1"

Please provide a set of concrete steps to reproduce the issue.

Expected behavior

X (IO Int) is not equivalent IO Int , cause we have type X a = a only for Eq types

Environment

• GHC version used: 8.8.4