Word highlighting in search and replace is unpredictable

Start with the following text in the editor:

```
This is a test.This is a test.This is a test.This is a test.This is a test.This is a test.This is a test.This is a test.
```

Press the 'end' key to position the cursor at the end of the line.

Open the Replace dialog and type "this"

I would expect either all occurrences to be highlighted, or perhaps the first one. In this case it seems to randomly choose the second instance:


Reproduce the issue in the editor using the provided text, cursor position, and Replace dialog steps, then trace the search-and-replace highlighting behavior. Done means the selected occurrence is deterministic and the reported example has a regression test covering the expected behavior.

Written by the indexing model from the issue text.