I was just burning a data DVD in Brasero, and the following dialogue popped up.
Ah, I get it. It’s negative because the data is going out of the computer and onto the DVD. Still not sure why it thinks I’ve got 2 billion megabytes though… 😛
How many megabytes?!
Jonathan Gazeley 
I’ve seen similar from total copy (an alternative to copying files using wndows explorer – which can actually count!). It got really confused when moving a single file of more than 4Gb. Once it got past the first 4 t went into negative, and started countng negatve too. Confused the hell out of me. Still worked though 🙂
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