Invalid synchronization of resources

I have written a DSL with Xtext editor associated to.
Many times, I have the editor show up errors in my DSL code and the package explorer not (see the attached figures).

Examples of errors are:

• "Type mismatch: cannot convert from boolean to boolean"
• "The return type is incompatible with equals(Object)"
• "&& cannot be resolved."

The compiled code is free of error. Closing the editor and opening it clear the error markings in the editor, of course. Or when I enter a space character in the editor, remove it and save the file (it means that no change was applied to the file content at all); the editor's markers are removed from the side of the editor. The error markers in the editor becomes consistent with the error markets in the package explorer.

I cannot provide a small project for reproducing and testing this issue because it appends unpredictably.

This issue exists since Xtext 2.6 (the first version we have used) and still valid with Xtext 2.11.
We have also encountered this issue with other DSL: Xtend, and Jnario.

Preliminary discussion: https://www.eclipse.org/forums/index.php/t/1085919/

No source file, test, or reproducible project is identified. Start by reviewing the linked preliminary discussion and the reported editor/package-explorer marker mismatch; done means reproducing the stale diagnostics and making the editor markers consistently reflect the compiled resource state.