change file name without selecting the file extension

Hey everyone.

I recently came across this strange problem. Since a clean installation of Mavericks when i try to rename a file the extension get's selected as well. It doesn't happen with all files. For ecample it happens with .srt files but not .mkv files. My macbook has no issues at all. I tried to find if there is an option in any preference panes but did not find anything,

Should anyone have any idea i would greatly appreciate it.

Many thanks in advance,

John