Pretty printer bad formatting

When compiling with -fwarn-incomplete-patterns, the first test case s17.hs (attached) outputs unmatched patterns correctly.

test.hs:4:1: Warning:
    Pattern match(es) are non-exhaustive
    In an equation for `f':
        Patterns not matched:
            B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _
            B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ A B
            B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ A B B _
            B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ A B A B
            ...

However, when compiling s18.hs each argument is printed on its own line. 16 lines of the output are included below.

test.hs:4:1: Warning:
    Pattern match(es) are non-exhaustive
    In an equation for `f':
        Patterns not matched:
            B
            _
            B
            _
            B
            _
            B
            _
            B
            _
            B
            _

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	lowest
Resolution	Unresolved
Component	Driver
Test case
Differential revisions
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