Pitch of samples change upon reopening a saved project

When I use samples in a project, I adjust their pitch by setting the time stretching mode to Auto for the sample and raising or lowering the tempo of the project. However, when I save a project, close it, and open it again, the sample automatically reverts back to its original unaltered pitch. Is there any way to correct this, as well as preventing the automatic change in future projects? Thanks so much.