this happens after a short time, mostly after text entering (latest version i used)
Thank you very much for the additional information.
Unfortunately, there is very little we can do. Unlike what you seem to think, yEd does not perform the actual rendering. This (as well as any special handling for multiple displays) is done by the Java runtime environment. As a result, problems like these have to be fixed in Java. If you are technically inclined, you can file a bug report with Oracle for this issue. (Since we cannot reproduce the issue and have almost no knowledge about your system, we do not have enough information to file a corresponding report.)
I have now a second tool which has the same bug. Only these two java applications have it. Very strange.