Yes true, even less than 80% and in some cases it went beyond 100% by another 100%. !
In fact progress bar has nothing to do with application processing it only counts the time elapsed from aAOR on a 6 month basis.
Once you login to your account click the question mark next to progress bar.
Also check below statement by CIC
https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1441&top=3
Totally useless tool for us as it indicates nothing, i believe this was created to obstruct candidates inquiries. Now you feel obstructed to make an inquiry with 25% progress. They say unless we exceed 6 months processing time try not to make much questions

GL