No, this was a feature request for OO clients and Online Document Converter, not a bug/issue
although when exporting PowerPoint to PDFs, the file size is much larger (larger than .pptx in most cases) compared to LibreOffice and PDFs converters
Reported on The same document,why onlyoffice convert to pdf much larger than msOffice to pdf, will continue the discussion there because this post was not meant for it