One-way syncing works now in such a way that the local side is used as a cache:
local data is only changed if different from the PBAP side.

Because PBAP does not support incremental syncing at the moment, all contacts
need to be retrieved before comparing against the local cache. That comparison
is done by the libsynthesis sync engine, as in any other local sync in
SyncEvolution.

For more information, see
http://search.gmane.org/?query=PBAP&group=gmane.comp.mobile.syncevolution

Merged into master, will be in 1.3.99.1 (= first 1.4 pre-release).