I'm running latest MyDMX(same as from web site) and I am unable to replicate this issue, with or without the dongle plugged in. Took me a bit to figure out how to be able to access "preset" mode(was easier than I thought). Two fixtures used a profiles I had to make. The rest are ADJ fixtures, no tweaks needed. Worked fine.
What's your computer specs, OS, Service pack, memory, storage(space available as well). Latest updates? Using a broadband router on your internet connection?