This was a new feature added to 3.8.4 to support custom project deployments for app servers that support specially named projects, like JBoss and it’s support for RAR, SAR, LAR, BLAR, etc. etc. files. This way if you have a dot in your project name, MYEclipse will honor the name of the project and deploy it appropriately, so for example:
Persistence.sar
will ge deployed correctly as a SAR file to JBoss, as opposed to the old way which made it Persistence.sar.jar which caused it not to be found or loaded by the app server.