Why does the preset no. keep on flashing after I have pressed LOAD?
The preset no. will continue to flash if no preset has been stored in this preset number (ie the preset slot is empty). This is because the M300 / M350 comes without any presets stored in the preset slots (See also this FAQ: Where are the factory presets?).
Try to store the current setting by pressing Store for a few seconds. Press Arrow up to the next preset, press STORE for a few seconds (to store another preset), press arrow down (the previous preset number flashes), press LOAD and it will stop flashing.