When creating a component for a project, it is not possible to manage multiple versions for this component. Instead, versions can only be created project-wide.

Example:
Component A exists in versions 1.0.1, 1.0.2
Component B exists in verstion 3.2
Component C exists in versions 1.6.2, 2.0

This issue was also commented here:
http://jira.atlassian.com/browse/JRA-12241?focusedCommentId=150002&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#action_150002