Discovered this during integration testing. Because Arrow-C++ writes buffers padded to 64 bytes, they may appear larger to the Java library than they need to be. In ListVector.loadFieldBuffers, the ArrowFieldNode is never used:
The value count of the resulting ListVector is thus inferred from the size of the offsets buffer. In the case of a length-7 vector in C++, the size of the offsets buffer is exactly 64 bytes (padding for SIMD) – Java infers from 64 bytes that the value count is 15 (64 / 4 - 1), and the integration test fails.