Solr findings do not care about pages the language has changed manually

Some pages were created accidentally using the default language English.
Enabling the multilingual feature and a second language, allows to change the language of a page.
This was made for all “English” pages.
Now all pages have the language setting “German(Germany)”.
Switch back the language settings to mulitlingual=NO and only support for German(Germany) leads to the situation, that solr does not find anything (in pages switched from English).
Adding English to the supported languages, will force solr to find results but they are displayed as findings in English pages and all results are marked with “foo (en)”.

After switching the search engine to database, all works fine.

Is this a bug or does solr use a old search index?
(using XWiki 14.5)

Regards Rainer