This is my experience in Roundcube 0.9.0.
I try to export and import a full address book.
The address book has 316 entries some of which are perfectly categorized into 8 Groups Under the main heading of Personal addresses.
When I do a full export I lose the subgroup categories. I can export the subgroups one by one but then I cannot re-import them the same way, only the first group will populate, the rest of the imported contacts go under the Personal addresses.
Any ideas?