Steps to Reproduce

Android

1. Create a TextField
2. Enter "abc def ghi"
3. Long press on "e" to highlight "def"
4. Move the touch point to "h", "def gh" is selected as expected
5. Move the touch point to "a", the space between "abc" and "def" is selected.

iOS

Double tap drag has not yet been implemented (tracked in #23973), but RenderEditable.selectPositionAt seems to work only in one direction.

Expected:

5. On both iOS and Android, move the touch point to "a", "abc def" should be selected. Also the initially selected word "def" in step 3 should always stay selected after step 3, regardless of the touch point position .