OneDrive Client Status Dialogue Box Shows two File Sizes - the actual size and "something else"

What is the meaning of the file size in parentheses when a file is uploading to OneDrive.

For example:

    FILE.TXT

    __________________________________________________

    UPLOADING 220.9 MB of 299.4 MB (158.5 MB)    (italics and red highlighting added by me for emphasis).

299.4 MB is the actual file size on local disk.  What does the 158.5MB number represent?

Thank you,