Your two Windows installs and user accounts will have different security IDs associated with them. If the data drives are formatted NTFS (and they usually are) the ownership/permission to access the data files will depend on which Windows 8 install and which user account you used to create or manipulate the files. You can try creating a FAT32 partition to share data, which won't have the same security issues but is a less robust file-system than NTFS. Recycle bin problem is due to the same issue - they're system folders and one OS isn't allowed to access the recycle bin created/used by the other.
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