What versions of Openfire and Spark? Are you talking about a group chat room or a one on one chat? I don’t see such issue with the latest Openfire and Spark versions.
It may be worth it to try with the latest 2.8.2 version or at least 2.7.7 (last for 2.7). You can download any version by changing numbers in the download address. Maybe you can find some clues in the logs.