This is a regression from the change to the new text fields. To reproduce, click in the middle of a text field and drag down. Note that it selects from where you began to the beginning of the field. But it should select from where you began to the end of the field instead.
I see the same problem in reverse with RTL fields.
This is almost identical to bug 8116.
These are all text field regressions so they should all be P1.
I'll take a look at these.
Presumably another Selection::adjustForEditableContent problem.
I fixed this, but it doesn't fix all cases of bug 8116.