You’ll find that LingQ Support is well aware of this issue, see eg:
My example word was ironically Việt Nam 
Feedback I’ve had is that they are looking at how improvements could be made, but that was a few weeks ago and I’ve heard nothing further.
But I agree that this issue really is almost a deal breaker. You start off thinking that it only affects a word here and a word there, but honestly the cumulative effect when trying to learn a monosyllabic language like Vietnamese with LingQ becomes endlessly frustrating and time-wasting. It’s so demotivating, which is really sad when I’m otherwise very keen and willing to spend time on learning the language.
As an aside, I do see this comment that some languages like Vietnamese are still in the beta category, but I’ve never found out where this is documented anywhere. Is there a list somewhere of LingQ beta languages tucked away? And does it have any specific implication other than the usual generic meaning of beta? For example, I can see that the Ministories are complete (though I have criticisms of the translations), but there are no courses as yet. I wonder what else is missing?