TnT and Nether Portals make for the Ultimate Griefing Tool

This issue is pretty self explainatory. Recent changes to the way nether portals work allows entities to generate a new portal if there is no portal blocks within the search radius in the other dimension. TnT is an entity, TnT can also destroy portal blocks, so if the player simply sets up a dispenser feeding into a nether portal and spams TnT into the other dimension it will create a chain reaction of portals generating and being destroyed allowing the entire search radius to be blown up and replaced with empty obsidian portal frames.

Included are screenshots demonstrating the process and the kind of damage it can create.

The mechanism of entities being able to generate portals is quite powerful and useful with respect to farming and automation so many players would be rather annoyed if this behaviour was removed. A well compromised solution may be to make portal blocks blast proof so that the TnT at least cannot destroy the portal blocks and force new portals to generate out of control like this.