Email signature not appearing consistently in OWA

We have a user that has his signature set up properly in OWA but it is not consistently being added to new messages that he creates. I tried clearing his browser cache and that did not fix the problem. I haven't had him try it yet in another browser as I don't want him to have to change his default browser just for this. I believe he's using Chrome as his default. Any ideas as to what could cause this? It seems to be intermittent, which makes it hard to troubleshoot.