This is the expected behavior of pipes[0]. A quick look at Lists [1] clears up how you can control this a little better (+Job Control). jamesdutc also linked to sponge, which may suit your usecase as well.

  [0] https://www.gnu.org/software/bash/manual/bashref.html#Pipelines
  [1] https://www.gnu.org/software/bash/manual/bashref.html#Lists