Disappearing functions?

My high school students are using Alice for the first time with generally good results. Some buggy behavior but all manageable, except for "disappearing" functions. About 30% of my students report successfully composing their own functions, but not being able to edit them. The button for the function is not visible in the details side-bar area, nor is the tab visible in the editing area. However, the function still runs; they just can't edit it's code.

Any thoughts? And thanks.