Why list view UnChecked items appear like Checked on scroll?

I have a custom ListView (TextView, CheckBox). Some of the items are checked & rest of them are not.

My problem is, when I scroll fast up/down ListView items appear like Unchecked items are Checked & on stopping scroll they get back to original state means become Unchecked.

e.g Item 1, 2, 3 are Checked & Item 4, 5, 6 are UnChecked. So, when I scroll fast it appears like Item 4, 5, 6 are checked for fraction of second & immediately gets Unchecked as they are.

I know getView() handle all this but my tester is keep posting this bug & I have to fix it. Please help me. Not posting code as it is a basic custom ListView. Moreover, i tried googling to find out such cases but nothing found yet so posting question here. Thanks in advance.