Invalid namespace importing Avro files generated from Protobuf

An error occurs when importing Avro files into BigQuery.
The files were generated using a ProtobufData schema.
The error shown is similar to:

BigQuery error in load operation: Error processing job
'<some_job_id>': Error while reading data, error message: The
Apache Avro library failed to parse the header with the following error: Invalid namespace:
some.package.SomeClassProto$

When using a modified version of the ProtobufData class, that yields a namespace like

some.package.SomeClassProto

(without the dollar), the import worked without errors.

Potentially related to AVRO-2143?