monaco-editor version: 0.20.0
Browser: Chrome
OS: Windows

Reproduction steps:

• Go to playground

• Paste code below

• Run

• ctrl + MouseOver on IdentifierA in line 1
  => Identifier A is blue and underlined; small widget pops up showing reference "another IdentifierA" => OK!

• ctrl left click on IdentifierA in line 1
  => IdentifierA in line 3 blinks and Cursor jumps to line 3 => OK!

• ctrl + MouseOver on IdentifierB in line 2
  => Identifier B is underlined; small widget pops up showing reference "another IdentifierB" => OK!

• ctrl left click on IdentifierB in line 2
  => Nothing happens. Editor should display model2 and Curser should jump to line 1 => Bug!

I was able to fix this bug:
a) insert
editor.setModel(model);
in standaloneCodeServiceImpl.ts after line 43
b) replace
return null;
whith
return monaco.editor.getModels().find(model => model.uri.toString() === resource.toString());
in Method StandaloneCodeEditorServiceImpl.findModel

Instead of b) it would certainly be better to use SimpleEditorModelResolverService, but i don't know how to get a reference of it so i better refrain from making a pull request on base of my amateur work.

By the way:
I'm writing an online-IDE with compiler for my students. Without monaco editor this would not be possible:

Monaco editor is an awesome library, thank you!

Editor Playground html:

<div id="container" style="height:100%;"></div>

Editor Playground css:
none

Editor Playground js:

const editor = monaco.editor.create(document.getElementById("container"), {});

const model1 = monaco.editor.createModel("identifierA\nIdentifierb\nanother IdentifierA", "python", monaco.Uri.from({
    scheme: "inmemory",
    path: "file1.macc",
}))

const model2 = monaco.editor.createModel("another Identifierb", "python", monaco.Uri.from({
    scheme: "inmemory",
    path: "file2.macc",
}))

editor.setModel(model1)

monaco.languages.registerDefinitionProvider("python", {
    provideDefinition: (model, position, token) => {
        if (position.lineNumber == 1) {
            return {
                uri: model1.uri,
                range: {
                    startLineNumber: 3,
                    startColumn: 9,
                    endLineNumber: 3,
                    endColumn: 20
                }
            }
        }

        if (position.lineNumber == 2) {
            return {
                uri: model2.uri,
                range: {
                    startLineNumber: 1,
                    startColumn: 9,
                    endLineNumber: 1,
                    endColumn: 20
                }
            }
        }
    }
});