When loading and unloading filament, there is no cancellation-button. Also i have not found any way to move the filament just a little.
When unloading filament, i have had the filament stop due to the end of the filament being a small blob. i have then removed the ptfe tube from the extruder driver side, but the blob is to far in for me to reach with my cutters, so i need to feed the filament out a little. Being able to do this with either loading and then cancelling, or by manually feeding a little bit would be handy.
I am not sure if this is something we could potentially change ourself, i have not dove into the marlin side of the printer, but if someone would add that functionality, that would be neat.
I did some investigation on this. From what i could feel the PTFE-tube was pushed all the way in, there was a distinct stop. However i found out that the PTFE-tube was cut at a slight angle, this could possibly have led to some leakage outside the tube which caused the small blob to form. I cut the PTFE tube straight with a razor and the unload after that worked great.
Maybe your PTFE tube is not pushed all the way into the hot end? If gap, this could be cause of blob.
I just use the release lever on the extruder to load or unload filament. I only have one of two heads working (solenoid failure), but doing this methods I have done multicolour prints on this printer. Make sure hot end up to temp.