Windows Search records an error message to the system log, when working on "NTFS" disk created with CBFS.
When CBFS filesystem name is set to NTFS, Windows starts to use some features specific to NTFS and not supported by CBFS at the moment. In particular this involves a change journal. As the change journal is not present, Windows puts an error record to the system log.
Using FAT, FAT32 or custom filesystem name tells Windows not to use NTFS-specific features and the problem does not appear in the first place.