The example found went up to 192% when hitting the 100% mark before success message was shown.
1) As portal admin choose a user with a lot of documents (555 in this example with a final zip of 1.4GB)
2) Go to Users in control panel, search for their ID
3) Choose Export Personal Data
4) Note this triggers an export process that could take some time
5) Leave the screen up and wait for progress bar to start moving
100% is displayed just before success
100% is reached but carries on while process is finishing causing percentage to ramp up over 100%. Some time is passing between 100% and success resulting in an additional 92%.