?Just not allowed in patterns in parentheses

The current parser does not accept ?Just in patterns in parentheses:

Start = (?Just 5) =: (?Just _)

The error message is: Parse error [sandbox.icl,3;22,pattern]: <pattern> expected instead of ?Just.

With a normal ADT this works fine:

:: X = X Int
Start = (X 1) =: (X _)

Without parentheses it also works fine:

Start = (?Just 5) =: ?Just _