Sync more than one database to the iPad

I have a Global Inbox and several databases on the desktop. In the sync settings on the iPad, those databases all appear. I check the Global Inbox and one other database. The Global Inbox syncs, and the other does not.

If I uncheck Global Inbox and leave the other database checked, nothing syncs.

Any hints?

Every database has a special group called “Mobile Sync”. Files and folders (or replicants of them) which are in “Mobile Sync” will get synced with DTTG, anything outside this folder will not. Are there items in that group?