Since the JS is slow in IE6/7, the JS addition of the X, warning, or check icon tiles across the entire message box momentarily during load.

Changing the last couple lines of popup_msg.css would stop the tiling problem.

Change:

div.status {
  background-image: url(status-info.png);
}
div.error {
  background-image: url(status-error.png);
}
div.warning {
  background-image: url(status-warning.png);
}

To:

div.status {
  background: url(status-info.png) no-repeat;
}
div.error {
  background: url(status-error.png) no-repeat;
}
div.warning {
  background: url(status-warning.png) no-repeat;
}