GHC accepts program with incorrect layout

GHC accepts this program:

f x = case x of
     False -> do
    { return x; }

but according to the Haskell report the implicit { opened by the of should be closed before the explicit {.

The bug does on to say, in a comment:

Update: arguably this should be allowed.  The fix to the Haskell
layout rule to allow it is simple: in Section 9.3 in the rules that
govern the introduction of the <n> and {n} psuedo-tokens, we need
to prevent <n> being inserted before {.  This could be a simple
side-condition on the rule that introduces <n>.

I can't see a Haskell' ticket for this at first glance.

Trac metadata

Trac field	Value
Version	6.6
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Parser)
Test case	read027
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Operating system	Unknown
Architecture	Unknown