The plot thickens further.
On both current and rc builds, Wireless Wire has an issue at any MTU over 1704.
To replicate, set L2/L3 MTU on Wireless Wire eth1 and w60 interfaces to Nominal MTU. Send a packet through the bridge larger than Actual MTU, and the link will go down.
Nominal MTU — Actual MTU — Differential in bytes
2290 2264 26
2284 2264 20
2276 2256 20
2264 2240 24
2024 2000 24
1812 1790 22
1758 1736 22
1732 1712 20
1720 1704 16
1712 1704 8
1706 1704 2
1704 1704 0