A bug I have noticed is present in regards to selecting items via keyboard. In explorer, if you hold down the control key, you can border highlight other items using the arrow keys. You can then add (or remove) that highlighted item to the selection using the spacebar.
the border highlight
selecting with spacebar
Holding down control and using the up/down arrow keys doesn't appear to work in multicommander. Some people might consider this a feature suggestion, but this functionality has been around since the xp days for explorer, and I would think is a core component of any explorer gui.