One, you cannot "build pressure" in a vessel that is not well sealed. In front loading washing machines in addition to the dispenser drawer there are other ways for pressure (if it ever built up to such a level) to be released. We know this from how suds/water will come pouring out of dispenser drawers and or door porthole.
Two, most modern front loaders with electronic controls have sensors that detect when something isn't right and machine will either abort cycle, drain water and or via other means let user know something isn't right.
Yes, hydrogen peroxide as it decomposes will liberate oxygen (and water);hence the prohibitions against mixing up solutions and leaving them in a *closed* container that is well sealed. Again your washing machine likely would give off the excess froth via methods mentioned above that would take down much of said pressure.
Can pressure build to the point of a washer exploding open? Well yes, it happened at local laundromat where some daft woman poured chlorine bleach *and* ammonia into the washer. But that reaction is far more violent I should think.
For very 10°F rise in temperature doubles the chemical action of peroxide bleaches. This *may* damage colors but usually with today's colourfast fabrics even boil washing temps with oxygen bleach wont' cause much harm. Provided it isn't done routinely and or too long.
With Oxiclean and other *cheap* oxygen bleaches the larger worry is they are often made up with large amounts of alkali (washing soda, sodium metasilicate, etc...). Alkali will enhance oxygen bleaching but also the increased pH can do a number on textiles.
