These help article supplements the notes that have been provided as part of the beta test and relate to the changes made to sketching within the app.
When moving a point, either with your finger or with the ruler, do not allow the resulting line to overlap another line, on lifting your finger, the point will be moved back to it's starting point.
When adding a point that would close a completely internal room.
Double tapping on a point close to the start of a room, undo could cause the app to exit.
When changing a line length using the ruler, if the line is extended so that closes a completely internal room, Undo was causing the app to exit.
When adding new lines, extra shortcuts are now shown.
See the diagram below, these shortcuts are at the intersection between a line at right angles to the last line (Line C) and the extension to other lines (Lines A & Lines B).