index hint returns wrong results

Am I missing something or is this a bug? Using an index hint returns the wrong results. Does it matter if the table is partitioned and the index is global or even what fields are in the index? I can't see how any of that should matter. The results should be the same:     

select /*+ index(t1 ind1) */ count(*)
from scott.t1
where f1 = 'one' and f2 = ' ';  

  COUNT(*)

         2

select count(*)
from scott.t1
where f1 = 'one' and f2 = ' ';

  COUNT(*)

         1

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