Bukkit

What steps will reproduce the problem?
1. Go in or create a protected region (by WorldGuard), where fire-spread is disallowed
2. Shot a fire arrow on a half step or a fence or any other transparent block in the region
3. Wait until the arrow burn the block down

What is the expected output? What do you see instead?
The transparent block, which burns would be deleted after the fire stops

What version of the product are you using?
V 0.91

Do you have an error log of what happened?
No.

Please provide any additional information below.
The plugin use a function to replace the block, where the arrow strikes, with a fire block. This must be changed by transparent blocks to save protected regions.