I feel like all these issues are handleable, but the damning issue is #3: they need space to move into. Labels can’t go away and need to be readable at all times, so a floating label pattern doesn’t actually save any space. You could have just put the labels where they float to to begin with. It’s still a neat effect, but it doesn’t buy you anything and may just cost you something.
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Floating Labels are Problematic is a post from CSS-Tricks