list traversal and remove

[digisatori at gmail.com]

I supposed the below code will print seven 2 and generate the list li
without 2.
Strangely it only print  four 2. If you change the number of 2 in the
list, the results are all beyond expectation.
I know the other way to achieve the expected goal, but why this is
happening? Could somebody enlight me?

li= [2,2,2,2,2,2,2,3,4,5,6,7,8,9]
for x in li:
    if x == 2:
        print x
        li.remove(x)