Seemingly can't mix ImplicitParams in where clauses

These are fine

v = () where
  a = True
  b = 'a'

v = () where
  ?a = True
  ?b = 'a'

but the moment one of them is an ImplicitParams variable as well as a regular one, it fails to parse

-- tAMA.hs:9:3-4: error: Parse error in pattern: ?b
-- Compilation failed.
v = () where
  a  = True
  ?b = 'a'

-- tAMA.hs:9:3: error: parse error on input ‘b’
-- Compilation failed.
v = () where 
  ?a = True
  b  = 'a'