Typically while standing near a Nether portal, when the "portal" sound plays, the sound fades when the player moves away from the portal. However, when using a custom sound in a resourcepack, it does not fade like it is supposed to. It is possible this bug may affect other sounds as well, but I have only noticed it here.
I also tested this on version 1.12.2, and both sounds functioned normally.
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We're tracking this issue in MC-146721, so this ticket is being resolved and linked as a duplicate.
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