Tried with current 5.* dev on Windows 10.
Entry preview looks nice.

But when I use the search field e.g. keywords=lesen or author=nord then it looks like this.

Issues is from the search highlighting of the search term. When you stop searching it's back to normal
The highlighting is handled by this simple javascript code:
I know nothing about JS.
What does your last post mean? It is easy to fix or the opposite?
I have tried if this issue still remains in the master branch and not only does it lose formatting, it also jumps to the Author field automatically, so I am rewriting my Author after search finds a result.
The formatting goes back to normal when I click to other article, not after finishing search, as @Siedlerchr said.
I would like to look at this issue and fix it.
The problem is probably that we read the inner text (i.e everything without formatting) and then set it as the inner html. Should work if document.body.innerText is replaced by document.body.innerHtml
@tobiasdiez It is not that easy. That's what I did before. The problem is then that it displays and searches matches in html tags
This should be fixed in the latest development version. Could you please check the build from http://builds.jabref.org/master/. Thanks! Please remember to make a backup of your library before trying-out this version.
Confirmed. It is fixed and working for me.
Thanks a lot.