There's a simple test is you think you have dirty power on the 512k, grab some big caps (1000uf or so) and stick them on the voltage rails on the floppyemu, should give it much cleaner power

Had the same issue with a project i built in my electronics class in school a year or so back, microcontroller went crazy every time i tried to power up the board, after a week of literally checking everything on the board i tried putting a 1000uf cap over the power input, and it worked perfectly from then on. Turns out the power brick i was using wasn't so well regulated