As mentioned in Summary
in the Rss feed generated page after an export the lastUpdated div show the data of node creation while should be the last modified.

Steps to reproduce

Use for instance ezwebin install with demo content and update content of some nodes, make an rss feed export including the modified nodes.
Go to the exported page the default rss/feed/my_feed you will see that the lastUpdated div use the data creation and not the modified one.