Since 4.0, after a few minutes of use, I am no longer about to paste material into a footnote, or drop in a zotero reference. If I reload the document, the problem stops. I have the same problem on chrome and firefox. I am using Linux (Ubuntu). (I previously used the wrong language to describe the problem, which is not the browser cache.)
Is this on fiduswriter.com? Or another server? Most likely there should be a JavaScript error report then.
Apologies for the delay. This is on fiduswriter.com.