C# 7 pattern matching for dynamic types

Consider the following code:

Microsoft.Office.Interop.Excel.Range myRange = this.Cells[1,1];
var myString = myRange.Value2 as string; 
if (myString != null)
{
 ...
}

R# prompts me to 'Use pattern matching' which results in 

if (myRange.Value2 is string myString)
{
 ...
}

while this gets compiled without a problem, when running MSbuild it throws a

error CS8121: An expression of type dynamic cannot be handled by a pattern of type string

From this post https://stackoverflow.com/a/41495614/839780 it looks like it's not supported properly.

I have to manually disable UsePatternMatching whenever it suggests it on dynamic types which is quite annoying.

Can this be fixed?

Thanks

P.S

This also applies to MergeCastWithTypeCheck for dynamic types