LinkageError: loader constraint violation: loader (instance of com/intellij/ide/plugins/cl/PluginClassLoader) previously initiated loading for a different type with name "org/jdom/Element"

I am developing a relatively simple plugin. Functionality that is called from menu action that supposed to get some JSON data from internet and write it to file worked fine.

But now it stopped working. I found that it happens after I add this extension to plugin xml:

<fileEditorProvider implementation="foo.MyLogicEditorProvider"/>

This class just adds another tab to JSON file editor under specific circumstances (specific file name). 

Any idea?