Warning
Fix for plugin copy patches a reference leak in cms.models.pluginmodel.CMSPlugin.copy_plugins, which caused the original plugin object to be modified in memory. The fixed code leaves the original unaltered and returns a modified copy.
Custom plugins that called cms.utils.plugins.copy_plugins_to or cms.models.pluginmodel.CMSPlugin.copy_plugins may have relied on the incorrect behaviour. Check your code for calls to these methods. Correctly implemented calls should expect the original plugin instance to remain unaltered.