XF 1.5 Member "upload a file" button?

Not sure if this pertains to just one member who made me aware of this or others as well, but I think it might be universal.
When he’s posting on the forum he has all 3 buttons “upload a file”, “post reply” and “more options”, however when replying to an in-box message or an alert, he doesn’t have the button “upload a file”, just “post reply” and “more options”, so he can’t upload photos. I checked permissions, style & browsing preferences, etc. As an administrator, I have all 3 buttons available in Forum threads, and in-box & alerts. Can you please advise?