Cache incoherency caused by duplication of documents in the cache.

When you load a document, you don't always know what language you want. Usually the getDocument() command is issued without any language and the storage engine is expected to get the document's default language. You ask the cache for a document called xwiki:Main.WebHome with no known language. When the storage returns the document, it has a language but the cache inserts it with the key from the original request.

When a document is saved or deleted, the actual document is passed to the cache and in this case it knows it's language. So the cache evicts the entry for
xwiki:Main.WebHome:en
But it doesn't know to evict xwiki:Main.WebHome
So the next time you try to load xwiki:Main.WebHome, the cache will dutifully return it because it doesn't know anything is amiss.