When you Download and add a new runtime using Preferences -> JBoss Tools -> JBoss Tools Runtime Detection -> Download it will install not only the newly downloaded runtime but also all other runtimes in the parent directory. This shouldn't happen as the user didn't ask for it.
Consider this scenario:
1. ~/runtimes contains a lot of runtimes
2. download as 7.1 and use the default install location ~/
3. when the downloading finishes not only as 7.1 will be added but also everything inside ~/runtimes

This probably happens because after the download JBT calls the search function in the install dir ~/. To fix this issue it could just call the search on ~/$NEW_RUNTIME_DIR .