@Rob: It sounds like the problem isn't expansion of the plastic but, as Brooks says in the article, the change in stiffness with temperature.
I'm not sure what material this door latch is made from, but often plastic parts that are designed to flex in operation are made from polypropylene. The elastic modulus of polypropylene changes by a factor of five between room temperature and 100°C, i.e. it is five times less stiff at 100°C than at room temperature. I'd guess that, even from room temperature to 90°F, it might change by as much as 50%.
The mechanical properties of plastics are highly dependent on temperature and strain rate. Design engineers need to keep these effects in mind. When designing a steel part, it's usually safe to assume that the elastic modulus, yield strength, tensile strength, and ductility are the same from room temperature to at least 300°F. With plastics, you can't assume that the properties listed on the datasheet are the same properties the material will have in your application.
Several years ago, Joseph Ogando wrote a great article for Design News regarding the use and abuse of plastics datasheets. It points out many of the parameters that affect the properties of plastics. I've sent it to a lot of people over the years as a reference.
Sounds like the hook should have been designed to be free of the plastic even as the plastic expanded. Even so, should the plastic on this microwave -- which is expected to get hot -- expand so easily? At merely 80 degrees? Seems the plastic may be part of the culprit.
Festo's BionicKangaroo combines pneumatic and electrical drive technology, plus very precise controls and condition monitoring. Like a real kangaroo, the BionicKangaroo robot harvests the kinetic energy of each takeoff and immediately uses it to power the next jump.
Design News and Digi-Key presents: Creating & Testing Your First RTOS Application Using MQX, a crash course that will look at defining a project, selecting a target processor, blocking code, defining tasks, completing code, and debugging.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.