RSRP-469149: Class 'this' is immutable" when assigning readonly field inside readonly struct constructor via "this.Field"

Just upgraded to R# 2018.1 EAP 6 (and VS 2017 15.6.5) and I'm now getting intellisense errors when assigning readonly fields inside the constructor of a "readonly struct".

If I change "readonly struct" to a regular "struct" (but keep the field readonly) the error goes away.

If I keep "readonly struct" but replace "this.Id = id" by just "Id = id" then the error also goes away.

–FAIL

public readonly struct Foo 
{ 
public readonly string Id;

public Foo(string id) 
{ 
this.Id = id; // ERROR: "Class 'this' is immutable. Cannot modify struct members when accessed struct is not classified as a variable" 
} 
} 

–OK

public struct Foo // not readonly 
{ 
public readonly string Id;

public Foo(string id) 
{ 
this.Id = id; // OK 
} 
} 

–OK
–FAIL

public readonly struct Foo // readonly 
{ 
public readonly string Id;

public Foo(string id) 
{ 
Id = id; // OK 
} 
}