Variable '_Vx44' exported from 'case'

[fogfish]

t() ->
   [option ||
      A =< case 1 of _ -> 1 end,
      B =< case 1 of _ -> 3 end,
      cats:unit(A + B)
   ].

Any match at case generates warning:

variable '_Vx44' exported from 'case' (line NN)

 30 t() ->
 31     case
 32         datum_cat_option:unit(case 1 of
 33                                   _Vx44 ->
 34                                       1
 35                               end)
 36     of
 37         undefined ->
 38             undefined;
 39         A ->
 40             case
 41                 datum_cat_option:unit(case 1 of
 42                                           _Vx44 ->
 43                                               3
 44                                       end)
 45             of
 46                 undefined ->
 47                     undefined;
 48                 B ->
 49                     datum_cat_option:unit(A + B)
 50             end
 51     end.