My operating system is linux mint, but I have had this problem on other versions of linux, and on different computers. I don’t use windows so I don’t know if it is a linux problem or not. My current version of libreoffice is: 5.1.6.2
Is it due to pasting in the some document or do you copy from another source (eg. browser, …)? In the past there have been some problems with copy/paste-functionality which was due to a nemo-bug. What is the linux-mint-version you are using?
If I paste from outside of libreoffice I have the problem. I have not noticed it when I pasted from one writer document to another, only when I pasted text from another source. My version of mint is 18.2, but I have noticed this bug for some time with other versions. If I paste from a web page the bug sometimes appears. If I paste from another program the bug sometimes appears. I don’t know if its nemo or not, but if I restart libreoffice the bug is gone for a time.