Some elFinder/elRTE bugs:

I installed elRTE, and the file manager. On first run file manager throws error: 

Invalid backend response.
Data is not JSON.

But Then it works normally. It throws this error when it doesn't find the datas/files folder, but just after the error, the folder is created and the file manager works normally without errors.

Additional bug:
There's a bug in elRTE: when adding images from personal file space, the editor gets duplicated, again and again every added picture. I used Chrome browser.
P.S. Also the style of image dialog looks odd - not like it should - the elFinder icon is not in place
P.S. 2 The buttons for adding color to text and background: don't work. After replacing the elrte.min.css from the original package, the color buttons started to work. So it has something to do also with that misplaced elFinder icon in image dialog.