I've made a slightly better picture here:
Thanks. And you get exactly the same behaviour in details mode?
Yes, details, thumbnails, tiles.
I am still trying to troubleshoot my issue.
I removed my installation and did a clean one with version 10.5. The point-select with CTRL works with the lister that comes with the installation but if I restore a backup (at any saved date in time i.e. between 2010 and today), the problematic feature stops working.
I first thought that it's may be one of my buttons that's wrongly configured so I played with their removal, to no avail. I then did the same with my (5) "personal" toolbars (plus a toolbar with the button Styles that came with Dopus, a total of six). If I remove one of my personal toolbar (any of them so the culprit is not a personal toolbar in particular), things work fine. I'm baffled and cannot think of anything else to solve my problem. Would it help if I can save my toolbars and send them to support? I just don't know how to save a toolbar one by one, only buttons. Thanks for your assistance.
If you want to PM me your config backup I'll see if I can reproduce it here.
Hi Jon, I just PM'd to you my configuration. Hopefully, you'll be able to find the culprit of my problem. Many Thanks.
Thanks for sending that! We've been able to reproduce the issue and will have a fix for it in the next update.
Thank God... Jon I mean 
What was the culprit if I may ask?
Amazing!.. o) Something new for the "fixed"-list.. o)
It was some complex interplay between the keyboard repeat rate and the number of toolbar buttons you have that potentially change state when the qualifier keys are held down.
Hey Jon - big fan of DO and I am having a VERY similar issue here. Ctrl + click does select, but often after 2 or 3 it then opens the files instead of letting me continue to select. Any iea?