You must be pressing some keys by mistake. Once you press F8 you are not supposed to press tabs, arrows, etc.
Rather than words, let us take the visual approach: The User manual has a few screenshots. See if your experience is exactly the same:
1. Page 91 describes how F8 looks like.
2. Page 113 (individual renaming) shows what controls can be used while naming/renaming. You may be pressing one of those keys while you are in certain pane (but not in the other).
(If you don't have version 1.4.0.0-2, delete the x2docs.pdf from the installation folder of x2 and press F1 in x2. This will automatically download the latest version from the website. )
BTW the official nomenclature for all parts of the GUI is provided on p. 21. There is no need to fumble for the most correct term!

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If you are sure that you are not pressing anything, but yet are getting these results, then click in the left folder pane (what you are calling "middle pane") and press CTRL+ALT+I. This will load the same folder as the other pane. Now press F8. Since you have the same folder in both panes, you should get identical results in both panes.