Badly uploaded images to browser

we have problems with badly uploaded images to our web application. It cannot be reproduced on local, but the problem is reported by clients. Images are cutted in some part and filled with random color(mostly grey) I attched exapmle images. Problem is on web part because our checksums are correct on server. This is not language problem it's occur on javascript and flex app. Files are also correct. In first attempt image was badly uploaded but when you try to upload it again it will be ok. We are not sure but maybe it's problem with memory or cpu is too burdened client's reported us the browser was acting weird. Is anyone had this problem or know source of it. Any hints will be welcome

Example image A Example image B