Native string should not be entered in Non Client.In other words, the IM shoud not work on Non Client. For my understanding, this is native string in German: üüpü+#äö and can be entered in Non Client.
This is reproducible for zh_CN as well. The steps to reproduce.
1. invoke IMFTest/IMFInputContextTest
2. type something in the panel of "passive(or active) client - private context"
3. move to the non-client panel
4. invoke Chinese IM
BUG: it's able to preedit and commit Chinese characters in non-client panel.

Note:
1. if "passive(or active) client - private context" is not focused. The non-client behavior is correct as expected. For this test case, moving mouse into the panel invokes the Focus event, so need to be careful when testing.
2. "passive(or active) client - default context" doesn't impact non-client.
3. only reproducible on Windows.