If you're getting munched while trying to get a big Ignite for Combustion, it will. Otherwise, no.
If you are trying to Impact Combustion, you have to wait a sec for Combustion to actually show up on the target first. There's a slight delay and with Combustion off the GCD, it's possible to pop Impact immediately after hitting Combustion, but before it shows up as a DOT to be spread. Any other instance of Impact failing is either a range/hitbox problem or a bug.
Guromin has offered to take over and update a new Mage Fire thread. If you have any suggestions or advice on what should be included, send a PM to him here. Once done, this thread (with an outdated OP and no longer maintained - I quit raiding a while ago) can be closed.
As Tyrian mentioned I am working on updating this thread. I wish I knew exactly when it will be finished, but I don't know for certain. I am allocating all of my free time to update the OP and I will likely have it finished within a week or two.
As Tyrian also mentioned, I am currently open to suggestions. Anyone with advice as to what should be added, changed or removed may feel free to send me a private message. I've already taken care of the obvious, but I would like to add additional information regarding Ignite Munching and Stacking. If there is anyone who is willing and capable of assisting in writing this section it would be greatly appreciated.
Thanks for your patience and advice as the thread undergoes construction.