Take the first screenshot listing all the installed extension from the main wiki, it display the Blog Application in version 3.5.1, while on the main 7.4.2 is installed, this is mentioned on the right. Now search blog, you get the second screenshot, where it list Blog Application 7.4.2.
Moreover (sorry I forgot to take the screenshot), if you open the details of the first listing (version 3.5.1), you get a list of the wiki were 3.5.1 is effectively installed. Why having choose to show me this version, I am on the main, this is not my version, just one this is installed on some wikis... but I have a wiki with version 4.1.4, and it is not listed here, neither is the blog app in that version.
So, my expectation from my understanding of the actual EM UI from the main wiki would have been to display the Blog Application as many times as I have different version of it installed, with according details for each, and not choose one of them. To not show button next to the one that is related to subwiki. Filtering only Main wiki application would be nice to have.
Nice to have too would be to be able to manage extension from subwiki in a centralized way, but this is another story (that you should keep in mind while evolving this however).