Playing instruments in the piano roll editor

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Sometimes it happens that I can't play separate instruments in the piano roll editor (the green button of the given instrument being on). This makes editing notes difficult, because I don't have immediate feedback. The notes are played when inserted in the piano roll editor, however, I must close the editor and play the instrument in the song editor to hear the whole melody.

Does anyone have an idea what I do wrong?

Thanks for help
Siloe
have an idea what I do wrong?
Nothing :p lmms is just not up to that, however i found a way partly around this 'glitch'*, and i made a yT video
http://www.youtube.com/watch?v=pFy8tipBbB8
It does not alow you to play on a keyboard, but does let you edit notes in playback-mode. Perhaps you use that?

*No glitch, if you experiment you can see that in piano-roll, the events for key-inputs are 'occupied' by actual note-events. If you hit a note when nothing is played, you do get sound, but not if the event is 'taken', and thats to be expected, so no glitch.

B.r.
Thank you! I have struggled with it for a long time and now I got it with help of your video :) I find also setting the loop useful, as it facilitates editing just a short part of the track.

Siloe