When I have selected Dual Horizontal view mode, I have noticed that when I want to select the folder tree title bar at the left hand side of the bottom pane in order to make the bottom pane active, I cannot do that. This was possible in DOpus 9. When I move my mouse above the left bottom folder tree title bar, the cursor changes to a double arrow cursor for changing the pane size. In DOpus 9 this was only the case for the upper area of the folder tree title bar. On the remaining lower area of the title bar the cursor was normal and I could then select the lower view pane. In the top pane it works as I expect it: I can directly select the top pane by clicking the top tree folder title bar. Is this a bug? I can now only select the bottom view pane by clicking the bottom right title bar, which I don’t find intuitive nor handy. I am using version 10.0.1.0 64-bit.
Clicking the tree header will (since one of the betas, and definitely in 10.0.1.0) make the associated file display active/source, so long as you don't click & drag to resize the panel.
Thanks Leo. Another quick reply 
It solved one of the most annoying issues for me since upgrading to version 10.0.0.0. I had waited for the first update before reporting this issue, but because the cursor look had not changed in version 10.0.1.0 I assumed the behaviour was still the same.
May I however make the suggestion to change this cursor behaviour? It is inconsistent with what happens in the header of the right bottom pane (where the double cursor only appears on the separation line) and Windows behaviour in general. I think users may get very easily confused when they see a double arrow cursor when they also can select the header. I like the way it is in the right bottom header (and version 9) better.
It's really the file display (bottom right) header that's the odd one out.
The file display header is different because it lets you click parts of the path, drag the panel's icon, and so it's easy/obvious you can click it to activate it, and so you can (if file display docking is turned on) drag it away to separate the two sides of a dual-display into two separate listers.
All the other panels just let you drag them to resize. Except for the oddity where you can click the tree header to activate the associated file display.
If we didn't have people used to the legacy behaviour, where clicking the tree header activates the file display, it would make more sense for clicking the tree header to activate the tree, but we can't change that now as people are clearly used to how it works.
FWIW, I was surprised that people were used to clicking the title above the tree to activate the adjacent file display, since the file display border is a much bigger and (at least to me) more obvious target, and the thing which is really being activated and changing color. That's why clicking the tree no longer did this in 10.0.0.0, but when a few people complained we changed it so you can click it again, while still allowing you to resize it as in 10.0.0.0.
Thanks (again) for your fast reply Leo. It made me investigate this issue further and I have now discovered that I can also click anywhere in the space in the left hand tree window, as well as anywhere in the right hand file window, as long as I do not click a file or folder. I guess I was so much used to Windows Explorer where clicking anywhere in the window also changes the folder/file selection, which is exactly what I do not want to do when selecting a window.
In reply to your "FWIW", the reason for me for avoiding clicking the file window header is when I have a long path I have to click all the way at the right part of the header. This is more inconvenient than just being able to always click the folder window header, or, which I have just discovered, anywhere in the white space of the tree window and which is as a matter of fact even better.
Thanks again 
There's an option in Preferences / File Displays / Border which makes the path 'hot' only when file display is the source and the Lister is active, so you are free to click anywhere in the header to activate the window and/or that half of the file display, without worrying about accidentally clicking part of the path.
(With that option on, when you do want part of the path, you just have to click twice.)