Please go here:
https://github.com/larskanis/fxruby/issues/2 I've created that issue in the FXRuby bug tracker, Lars Kanis, then maintainer says:
"This is actually a bug in the fox toolkit. If you set the FXText to styled=true, then the memory needed for getStyle is allocated. If not libfox crashes.
May you open a bug report on fox-toolkit? I'm a bit busy currently."