Hot swap a groovy class?

How comes that in IDEA I can never use hot swap during debugging to update a groovy class ("schema change not implemented")?
This happens even if for testing I recompile the groovy class without changing anything.

I started to do some baby steps in groovy in my Java app.
My hope is that code becomes more concise, easier to read and quicker to write.
However having to restart my web app for each tiny change eats up all the benefits that groovy might otherwise have.
(Groovy 1.6.5)