Before this feature was added, it was possible to right click to instantly open the context menu, and then hover over an item before releasing right click, and have that action be executed without a left click. This is still possible, but now the user must halt their cursor movement and wait for the menu to appear before doing this; this breaks workflow. The reason for this is that thunar gives you a short period in which you may drag the folder using right click, to choose between moving, copying, and linking the file to another folder. I believe this should be an optional feature for two reasons; the first is the reason I listed above, the second is that it's a potential accessibily issue; those with motor control issues might find it hard not to trigger the dragging action when right clicking.
When has this feature been added? I am not aware that this has changed (intentionally) recently.
I'm honestly not sure when it was added, only that it didn't have it before (I'm decently sure of this.) I think it may have been recent, can't confirm though. Regardless of when it was added I still think it should be optional.
Reading this again, I don't think it is a new feature and it has not been "added" unintentionally. Besides, as you described, it is still possible to do what you want if you wait only for a split of a second longer. No need to make this optional. Since we're going to port all of Xfce to GTK3 anyway, we will not change any established features until this has been achieved. Closing won't fix.
I wasn't saying it was unintentional, just that I think it should be made optional. Fair enough though.