Spanner end is not saved correctly

ae475eb0fd

1. Create a flute score and enter 8 quarter notes
2. Insert a text line on the first note
3. Extend it with Shift + right to the the second quarter in the next measure
4. Replace the first quarter of the second measure by a dotted quarter
5. Save and reload

Expected result:
The textline extends to the second beat of the second measure

Actual result
The textline extends until the end.

Discussion:
The MSCX doesn't have an endspanner tag since there is no segment ending when the spanner ends. What's the value of having an actual tag when the spanner ends? If we really need a spannerend, we could output it between two segments... with an offset.. MusicXML (and I believe Sibelius) uses a length for spanner. Why doesn't it fit in MuseScore model?