Time("J2000") and equivalents should be equal

I noticed this behaviour:

In [21]: t0 = time.Time("J2000", scale="tdb").replicate("iso"); t0
Out[21]: <Time object: scale='tdb' format='iso' value=2000-01-01 12:00:00.000>

In [22]: t0.jd1, t0.jd2
Out[22]: (2400000.5, 51544.5)

In [23]: t0.unix
Out[23]: 946727935.8160995

In [25]: t1 = time.Time("2000-01-01 12:00:00", scale="tdb").replicate("iso")
Out[25]: <Time object: scale='tdb' format='iso' value=2000-01-01 12:00:00.000>

In [26]: t1.jd1, t1.jd2
Out[26]: (2451544.5, 0.5)

In [27]: t1.unix
Out[27]: 946727935.8160994

In [29]: t1 - t0
Out[29]: <TimeDelta object: scale='tdb' format='jd' value=0.0>

In [30]: _.sec
Out[30]: 0.0

In [31]: t1.unix - t0.unix
Out[31]: -1.1920928955078125e-07

This is giving absolute differences of 1e-7. This difference may or may not be important depending on the specific application, but in any case are they expected? If yes, should they be documented? If not, what is going wrong?

[astrojuanlu]

Thanks @pllim, @mhvk. I might fix this myself this week if I have the time.

[astrojuanlu]

Attempt to fix: https://github.com/astropy/astropy/pull/6653