The drag selection is enabled immediately after dragging the cursor a little (1-2px). This causes issues when a row is expanded/collapsed first then clicking the checkbox as sometimes, the cursor is dragged in the checkbox. Then drag selection resets the previously selected rows. Here is a screencast of the issue:
The drag selection should not be enabled.
The Grid has a logic for enabling the drag selection after N-pixels of dragging. Could be reused in TreeList as well.