I've found 3 different senarios where this bug occurs. 

1) Player impacts target block while using a firework rocket with an elytra and then leaves flight mode. The target block then continues to output a redstone signal until the firework particles stop appearing on screen. This is most apparent when using a Flight duration 3 rocket.

2) Player impacts a block that is not the target block while using a firework rocket with an elytra , and then walks onto the target block. The target block starts outputting a redstone signal for the rest of the duration of the firework.

3) Scenario 2, but also switching to a chestplate during the duration of the firework. This was done to make sure the bug was concerning just the firework rocket and not possibly an interaction with the elytra.