It seems very intermittent. I just tried again with subject only and it didn't show up. I tried to refresh my browser screen after I did the attachment but that did not help.

It manifests itself as sending two attachments with the message because if you don't see the first one then you try a second time. The second one shows up and then you press send and it sends a message with the duplicate attachment.

It's more of an annoyance but there may be an underlying problem that is larger. Not sure.