Check the Single/Multi-Threading Support for Consistency
As a consequence of #164 (closed), the writing single-core and multi-threads differ. The multi-threaded version supports multi-writer writing at once but not for the single-threaded. This should be fixed. It does not create errors since we shifted completely to the multi-threaded version as the default. The split and merge of the multi-threaded writing should be better in all cases since the importer/export relies on the single-core functionality.