As frustrating as it is I don't think Hartlepool are to be blame - it sounds like they are simply exercising a contractual option. What is still unclear is whether or not Porter has any say in accepting, or not, the contract extension - Tony P, not surprisingly, doesn't know the details of the extension clause.
Hopefully it can be worked through but Hartlepool have obviously had plenty of experience of writing contracts so, if it is enforceable, I suspect it will come down to whether or not they want to "handcuff" Porter for the next season.