I have IPassword 3 on iOS and 3.8 on OSX (and a Windows version) These all sync across Dropbox.
I bought 1Password 4.0 for iOS but it could not find any of the existing files - first just giving a red mark against Dropbox and then on a later version giving text that Dropbox failed. Now with 4.1.1 it does sync with Dropbox but does not find my existing entries it has a new empty database. On startup it asked for permission to use dropbox and then said it could not find any fles on Dropbox.
I suspect it is the issue 2 in http://learn.agilebits.com/1Password4/iOS/Sync/Dropbox/stuck-dropbox.html However the top of this note says it has been fixed in 4.1. Thus I am confused the bug looks exactly like this one but you say this has been fixed.