Strange Kotlin error after update: Duplicate entry

Question

Please check code below:

class HTMLEngine : View {
    class HREFOffset(var YOffset: Int, var href: String)
    class ChapterHolder(var chapter: Int, var chapter_body: Node)

Kotlin compiler says :

Cause: duplicate entry: com/app/view/HTMLEngine$ChapterHolder.class

Update:

I reverted to 4.3.1, everything worked fine for a day, then again problem appeared. I doubt it's because of latest Kotlin plugin.