Having seen both sides of aviation training, as an ATCO and to CPL/IR, I don't think that the whole concept of clearance limits and why they exist is stressed enough during pilot training: it certainly wasn't during mine.
Unfortunately that means that there are many pilots out there think like Mentaleena. Either they don't realise the existance of a clearance limit in the first place, or they think that if a clearance limit is reached without a new clearance being issued, then it's OK to either continue with the FP or continue with what the controller must be expecting (assuming that the radio is working).
That scares the willies out of me as an ATCO.