Existing fires do not spread when fire tick is changed from false to true

Steps to reproduce

1. Create a new world.
2. /gamerule dofiretick false
3. Light some trees on fire.
4. /gamerule dofiretick true

Expected result

The fire spreads throughout the trees.

Observed result

The fire does not spread.

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I turned firetick off so I can set trees on fire and then turned firetick back on to watch the fire unleash but the fire burned indefinitely even when having a 500 tick sped game