Here's what I did: I made my own drum set with patterns from another project. Then I tried to make a song and I deleted all the bars in list of patterns in song mode. Now when I try to drag my patterns to this empty list, nothing happens...? In other words, I cannot make any bars with my patterns. I am using it in standalone mode and in mac OS X.
Maybe I found a bug here: If you delete patterns and press D few times "too much" you will have song made of negative
amount of bars. Then you'll get a song in which you cannot import any patterns.