I've just hit the exact same issue! It does look like a bug to me -- the area reserved for the clear button clips the placeholder to the right.
The workaround I've found it to change the clear button style to "always", which is a misnomer as in fact the clear button still isn't displayed when the placeholder is visible (i.e. when the text is empty):
textField.clearButtonMode = UITextFieldViewModeAlways;
It does mean that the placeholder isn't aligned fully to the right (leaving space for the clear button, even though it's not there), which would be fine if the clear button was indeed displayed! This can be fixed by somehow ensuring the UITextField always contains a space instead of a blank, thus forcing the clear button to always (and that means always!) display.