Another 1.5.24 to 1.6.1 migration question

[Chris Green]

I have another question regarding 1.6.1 differences from 1.5.24.  In
my index replies to message don't show their subject line correctly,
for example:-

        18 r + 10-May-16 Jane Chevous    (  83) Reshapers
        19   + 10-May-16 Jane Chevous    ( 179) M-b~T~TM-b~T~@>

That M-b~T~TM-b~T~@> should be the ASCII graphics 'tree' to the next
message in the thread.

I guess this is some sort of build configuration issue but I'd be
pleased for any pointers.

-- 
Chris Green