When a user right clicks in the chat window and selects Clear, he is presented with a dialog asking "Permanently delete". If he presses Yes, the window is cleared, but the history of that contact is not deleted. If a user opens a chat window with that contact again, the history is still there. This is happening with English GUI language, until a user tries to set some other language. Then after Spark restart if you open the chant window with the same person again it then shows blank history. From now on if you change back to English, it will delete history normally. There was a similar issue with 2.6.0, when Spark wasn't deleting the history with other than English GUI languages. Seems like the issue is still there in some other form.
Looks like it is deleting the history correctly now. Maybe the latest patch to history file hooks closing by speedy fixed this also.