Hello Balsamiq team,
I’m using Balsamiq Desktop (latest version) on macOS Sierra with a French BÉPO keyboard.
With this keyboard, writing an underscore requires to type Alt + Spacebar. This works perfectly on any app but Balsamiq… Instead I see spaces displayed in Balsamiq.
I know I have a very special configuration, but I guess any keyboard configuration should work with balsamiq so you might have a bug there.
Let me know if you need more details, I would be happy to help.