i find in general that people have the most problems recalling a terrier compared to most other dogs. in my opinion its mostly down to the early stages of training or should i say lack of it ( im not saying its the case with you pig nut, just a general observation )
a terriers drive is no stronger than any other working dog and is no less able to be taught to stay at heal or return on command, i think alot more time is spent on the recall with other breeds like , lurchers, spanials, labs etc etc..