To my knowledge, this is not a known issue. I would recommend sending this to our Support team at firstname.lastname@example.org. If you can include the workbook (saved as a twbx file) and/or screenshots showing how the tabcmd get is not returning the expected results will allow for a more timely response.
If an extract gets refreshed before you call get, it seems to fix this. This is a workaround.
You might also consider putting the string ?:refresh=yes a the end of your GET string ala "/views/workbookname/viewname.png?:refresh=yes" -f "viewname.png"
Thanks Russell ... that worked for me.