Shift + Ctrl + O (Source/Organize Imports) on package level messes up imports for groovy-files

When performing Shift + Ctrl + O on a package level all sort of imports get lost and useless ones like java.util.Date; or java.math.BigDecimal; is added (with a semicolon to the end). E.g. in my case imports for AST Tranformations (like import groovy.transform.EqualsAndHashCode) and even references to other groovy-classes were removed from my domain classes.