recording midi while in loop

that is all strange. once you set a loop range you certainly don't need to reset it over when you wish to engage in recording.

just try the follwing steps, which might seem overwhelming for a first timer but hopefully tend to get intuitive and obvious later on:

1. check that View/Options.../Transport/Loop recording mode (takes) is set to "First" or "Last", then set your loop range as usual, just once; you can also set a punch in/out range if you will, but that's not the point here now;
2. arm your MIDI track for recording (the [R] track button is lit red) and press main red button to prepare recording; if session is untitled new or blank it ask you the name that also serves as for file-name prefix;
3. connect your MIDI (piano keyboard?) controller output into Qtractor MIDI input port (you can do this whenever before, but here is your last chance);
4. make sure your MIDI controller sends on the same MIDI channel to the armed MIDI track, or you can check Track/Auto Monitor on and click or select the desired target MIDI track as current track (that will make all incoming MIDI filtered to the current track channel, automagically);
5. start playback so recording starts rolling... hit some keys, watch events being drawn under a red shaded strip while on the mixer strip the metters pump up and down as you're playing the piano keyboard keys; play as much as long for the play-head turn around a couple of cycles over the loop interval--each turn will be called and numbered as one take; hit stop;
6. now right-click anywhere on the resulting recorded clip and head for context-menu Clip/Take sub-menu, or you can just try pressing Shift+T to cycle between takes, starting from the one you chose on 1.

or else you can always find some more help on the qtractor wiki, this section in particular and, who knows, give a hand or two :)

hth.
cheers