If you install FCPX after FCP Studio your mac will bundle your out of date software into a nice FCP Studio folder.
If you install FCP Studio after FCPX your mac will overwrite FCPX. Yes this is annoying. But I guess it doesn't really affect many people.
Basically if you really do need to install FCP Studio after FCPX then you need to put FCPX in it's own folder. Here is a rather dull article on FCP installation best practise. Even writing that sentence was boring. Sorry.