Breaking a block of netherack that is on fire does not eliminate the fire on top of it, just makes it invisible.

To reproduce (this will occur in both creative and survival):

• Place a block of netherack. 
• Use flint and steel to light it on fire
• Break the block of netherack
  • Fire will disappear.
• Enter the space where the netherack was
  • player will catch on fire and take damage.
• Attempt to drop an item onto the top of the block that the netherack occupied
  • item will disappear
• Replace the block of netherack
  • fire will become visible again.

Expected result:

• When breaking netherack the fire should no longer exist as there isn't anything to maintain the flame
• The flame isn't visible so it should no longer cause damage.
• Replaced netherack should not be on fire before the player (or another mob) ignites it in some way.