Issue flattening streams of Time.diagram()-generated streams?

[mathieueveillard]

Please consider the two unit tests below, run with Mocha, where Time = mockTimeSource() (@cycle/time):

    it("Test of flatten (1)", function (done) {
        Time.assertEqual(
            Time.diagram("0----1----").map(i => xs.of(i)).flatten(),
            Time.diagram("0----1----")
        )
        Time.run(done)
    })

    it("Test of flatten (2)", function (done) {
        Time.assertEqual(
            Time.diagram("0----1----").map(i => Time.diagram("i---------", {i: i})).flatten(),
            Time.diagram("0----1----")
        )
        Time.run(done)
    })

The former passes, the latter fails:
Expected 0----1 Got (01)

This sounds in contradiction with the definition of flatten. Is this a bug?

Thanks

Mat (new user of xstream and cycle.js)