I have also encountered this and it is really annoying. I recall this behaviour being mentioned in the Apple docs somewhere but if it's by design then the design is broken. I have submitted a feedback request on this but I doubt anything will come of it.

You can keep tabs on the related issue here - https://github.com/xamarin/xamarin-macios/issues/10086/, where a recent post said: Our company has been in contact with Microsoft who in turn has been in contact with Apple. They've been giving us almost daily updates but haven't made any real progress. Both are aware of the issue, have reproduced, and are actively engaged in figuring out cause and fix. Given how easy it is to reproduce the issue, I'm surprised at the time it is taking Apple/Microsoft to figure it out.