IMFTest/IMFInputContextTest failed on Windows.

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.