When I edit the email templates, I loose the formatting after I have saved. When I try to send out an invitation, the text formattings are gone, and when I edit the email templates again, they are also gone.

What happens...?

Hard to say. Maybe you should first update to the latest version.

Yeah, I thought so too. So I am about to install the latest. I use 1.9.0 and not 1.9.1 for production, right?

Right

Hmmm. Same thing happens after update to 1.90... Any idea?

1. Please switch on debug mode by adding the following line to your config.php file:
Are there any additional errors reported on top of the page?

2. Does that problem also occur when changing just a single word?

I added the debug line, but I see no debugging info in the administrator yet.

Now the same error also happens in Edit Survey settings -> Welcome message

I didn't do any changes, I just opened the settings, and saved it again.

I have made a screen video, so that you can see what happens. The same happens in all windows where I enter a question or email

www.screencast-o-matic.com/watch/cXV0IllOq

Try to re-upload all fiels in binary mode, maybe a file was broken during file upload.

Also clear your browser cache and try using a different browser.

Well, I uploaded everything as a zip file, and then unzipped them on the web server. And the strange thing is that I have the same issue with two different versions of limesurvey on the server: 1.86 and 1.90.

I have limesurvey installed in a folder in the same area as a joomla site. Is there a possibility that there is a javascript or jquery conflict because of that..?