Strange watch behavior

This seems like a bug, but it's so weird, I'm not really sure what's happening. This is in 6.5.5 x64.

.NET Core version (host): 3.0.0
.NET Core version (queries): 3.0.0
Roslyn Version: 3.3.1-beta4-19462-11
FSharp.Compiler.Service version: 32.0.0.0

Here's the repro.

1. Create a new c# statements script containing only Console.WriteLine();
2. Set a breakpoint.
3. Debug to the breakpoint.
4. Add a new debug watch on the expression Math.Sqrt(1L).
5. Note that the resulting value is 2.2227587494850775E-162.

That's wrong... right? The long argument is supposed to be implicitly converted to 1.0d.