Wondering if this bug is new in Groovy 1.8.4; it seems it work better in 1.8.2.
The problem is that groovysh is throwing IncompatibleClassChangeError in a few cases:
import com.not.Found // import that doesn't resolve to class
show // command doesn't run at all
purge // command doesn't run at all
Groovy 1.8.4 appears to be working well, otherwise.
Please let me know if you need further info. It seems reproducible, here.