Cannot call `std.range.chain` with ranges of range of same ultimate element type

[Geod24]

import std.algorithm : map;
import std.range : chain, front, iota, ElementType;

immutable string Letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

void main () {
    // Range of string
    auto str = iota(20).map!(v => Letters[v .. $]);
    // Range of range of string
    auto ror = iota(10).map!(v => str.save);
    string[][] equiv = [ ["A", "B"], ["C", "D"] ];
    pragma(msg, ElementType!(typeof(ror)), " -- ", ElementType!(typeof(equi\
v)));
    pragma(msg, ElementType!(typeof(ror.front)), " -- ", ElementType!(typeo\
f(equiv.front)));
    auto result = chain(ror, equiv);
}

Yields the error:

% ldc2 ror.d
MapResult!(__lambda_L8_C30, Result) -- string[]
string -- string
ror.d(14): Error: template `chain` is not callable using argument types `!()(MapResult!(__lambda_L10_C30, Result), string[][])`
    auto result = chain(ror, equiv);
                       ^
/home/mlang/dlang/ldc-1.41.0/bin/../import/std/range/package.d(977):        Candidate is: `chain(Ranges...)(Ranges rs)`
  with `Ranges = (MapResult!(__lambda_L10_C30, Result), string[][])`
  must satisfy the following constraint:
`       !is(CommonType!(staticMap!(ElementType, staticMap!(Unqual, Ranges))) == void)`
auto chain(Ranges...)(Ranges rs)
     ^

I expect it to work, since ror is essentially a range of string, but the CommonType check seems to be too restrictive for this.

[pbackus]

What return type do you expect chain(ror, equiv).front to have in this scenario?

[Geod24]

Something that is a range of strings.