In a web site I have written I used to copy a table from Libreoffice Calc into ckeditor4 without problems (back in June 2019). Now it is copied as an image and an image is uploaded (image uploading has been working fine by itself).
Besides starting with a very basic configuration and adding features one by one I am clueless about this behaviour change. Going back to ckeditor 4.11.4 hasn't helped. I wonder if this is caused by recent browser changes as the ckeditor configuration has been stable.
Observed with: Firefox 70.0.1 on Linux Mint 19.1. Firefox 70 on Windows 10. MS Edge Chrome on Windows
Things work correctly with: Chromium 78.0.3904.108 on Linux Mint 19.1.
The issue should be resolved with https://github.com/ckeditor/ckeditor4/issues/3585 fix which will be available with CKEditor 4.13.1 version. The version which fix should be released very soon (i a couple of days). Follow https://ckeditor.com/blog/?category=releases&tags=CKEditor-4 for blog post about the release. If you will still struggle with the issue after upgrading to 4.13.1, report a bug on CKEditor4 Issue Tracker.