Is this an error in the OSCAL JSON schema?

[GaryGapinski]

When validating https://raw.githubusercontent.com/usnistgov/OSCAL/main/json/schema/oscal_complete_schema.json a validation error is found at line 4990 complaining «The keyword "contentEncoding" is ignored by the validation engine. It is either not part of the JSON Schema Draft 7 Specification or is used in conjunction with "$ref". ». The same error occurs in (different locations within) the sibling JSON schemata for the same Base64Datatype definition.

This was tested using <oXygen/> XML Editor 25.1, build 2023042509 for validation of JSON Schema documents. That documentation link indicates that JSON Schema Draft 7 is used for validation (due to the meta-schema declaration, which appears to have a trailing # wart).