http://bugzilla.zimbra.com/show_bug.cgi?id=11233
This looks like exactly what you are describing.
/dev/mapper/Ubuntu-root is long enough that df wraps
33576 2623 29249 9% to a line by itself.
Since zmdisklog parses for the 2nd and 4th fields, it gives the results you see.
I suggest going over to bugzilla and adding your 2 cents by voting for this bug.