Maybe it is just magic but it looks like to work so far.
Just try by yourself to find corner cases.
I will add comments here if/when I find issues with this configuration.
Set up sync with ownCloud. Now, on the Android device, add a new field which you do not already have on the contact stored on the server side (note etc) and sync. The new field will be transferred to the server, however the category of the contact will be reset to be empty.
Thanks for your report, but this is auplicate of #48. Please search through the issues before creating a new one.