Mixing New & Old Firmware

I discovered that my new LiteBeam AC with 3.25.2 firmware will NOT connect to another node running anything older than 3.18.9. Not by rf or dtd. The nodes appear on the mesh list but won't connect. Our mesh of 10 nodes is mostly legacy nodes but a few run 3.18.9 and 3.20.x which connect just fine. Luckily I found that 3.18.9 WILL work on the 32 Mb memory nodes, but I think I would be pushing my luck running anything newer (larger). We have a couple Rockets (64Mb) that have 3.20.x already. Hopefully this discovery will help someone who may be in the same situation. Little by little we hope to upgrade as many of the nodes as is financially practical, and a couple are not easily accessible.