Hi!
It's most likely a bug, this demo is based on an old alpha build and there may be still some old weird bugs happening in this version still (that we've fixed since then, but may be present in this demo)
Sorry about that! Hope that you still enjoyed the demo, there's only the first level anyway in this build, don't worry you didn't miss any content!
Sincerely,
InsaneHawk, creator of Rhythmy