I have filed this in our PR system. Thank you for the report.
You should be able to just delete the libraries that are added to your project and remove them from the WEB-INF/lib directory. Than, manually copy the 1.2 libraries from the com.genuitec.eclipse.cross.easystruts.eclipse_3.8.3\data\1.2 directory into your WEB-INF/lib directory and readd these libraries using your Java Build Path project properties properties.
If you don’t want to have to do this for each new struts 1.2 project, you could reconfigure the Struts 1.1 library defintions at Preferences > MyEclipse > Project Capabilities > Struts > Struts 1.1 to actually point to struts 1.2 libraries. Sorry for the inconveinience.