This is not a bug.
The sample is using on demand mode featurelayer. When panning the map, it forces to retrieve the features from server again. According to the screenshot you provided, the feature you are editing is still selected when you pan the map, which means the edits haven�??t been sent to server since the sample code only call applyEdits when the feature is deselected. So the solutions could be:
1. Use snapshot mode instead of on demand.
2. Call applyEdits whenever a vertex moves.