Fixed in 0.9.0, which made friends' movement roughly two-thirds less uneven.
Shippedstep 8 of 8
The host saw joiners' movement jitter. The cause was how each movement update was timestamped on the sender's side, not the receiving side. 0.9.0 stamps updates with the game frame they were read in, and a friend now carries on through a late update instead of freezing and leaping. On a local network in testing the unevenness dropped from about 36% to about 13%.
The steps
Queued · On the list, not started.
Looked into · Investigated or designed: the cause or the plan is written down.
Built · Written, with tests, waiting for review.
Reviewed · Passed code review.
Rig-tested · Checked on two real games playing together.
Merged · In the next release's code. Before the release goes out, the whole of it is played for several hours straight on two games, to catch rare crashes and problems that only show up over a long session.
Long playtest · In a test build of the release, being played for several hours straight on two games.