Custom FileType icon and filename disappear from Project View after some time

I created Custom Language Support plugin based on tutorial (http://www.jetbrains.org/intellij/sdk/docs/tutorials/custom_language_support_tutorial.html).

For my FileType I reuse StdFileTypes.PLAIN_TEXT.getIcon() like https://github.com/akrylysov/intellij-nsis/blob/master/src/com/krylysov/nsisplugin/NsisFileType.java#L38.

The problem that after some time working in IDE, icons and filenames of my custom language disapper from Project View.