That's default selection behaviour for all commander-style file managers.
I was going to complain about the crappy file-selection clicking interaction methods when selecting multiple files in Commander mode, where selecting multiple files then trying to revert back to a single file was extremely annoying and unproductive... but something prompted me to look in the prefs (I think I was about to switch to Explorer mode just to see if the problem existed there, before reporting the bug)
Low and behold, there I had found the settings for the Commander mode to use Explorer-style selection using mouse and keyboard. Very nice, but why can't that be the default? Do enough people want that buggy Commander-style of selection? It's so counter-productive!!