Sometimes when selecting and using tools in Expert Mode or Full Edit in older versions of Elements, they can behave differently to what is normally experienced. This can be due to a variety of causes, but the problem can often be quickly fixed with a tool reset.
How to fix
Select your desired tool, click the tool option menu (drop-down list) and choose Reset Tool.
For recent versions of Photoshop Elements you will find this near the bottom-right of the tool options bar.
For other versions (PSE10 and earlier) you will find the icon near the top-left of the tool options bar.