MineCraft 1.7.10
OpenComputers-MC1.7.10-1.8.2+94f6405-universal
JRE 8u371

I noticed the placement order of beacon and adapter will affect the whether the adapter can read the result correctly.

If you place the beacon first, then place the adapter, we can get correct result.

But if you place the adapter first, then place the beacon, the adapter will read the default value of beacon.

And even after 4 seconds, the result is still wrong.

Other vanilla devices like furnace, seem not have this compatibility issues.