dropbox self deletes from login items

[jayess]

If I add Dropbox to my list of login items (System Preferences) it will startup, as expected, when I next restart my computer (iMac, Yosemite), however I find it has then disappeared from the list of login items, other items remain in the list. Can anyone explain this extraordinary rejection of the Dropbox app?

 

[Mitthrawnuruodo]

In your Dropbox preferences, is "Start Dropbox on system startup" checked?

 

[jayess]

In your Dropbox preferences, is "Start Dropbox on system startup" checked? View attachment 563080

Many thanks, that preference was unchecked. I had mistakenly assumed that it was only necessary to enter Dropbox as a start up item in System preferences, I hadn't looked at the Dropbox preferences at any time.