I have the following situation: there's one folder which has around ten thousand subfolders, all of which have pictures inside them. I want the outer folder to have the List view and all subfolders to have Thumbnail view (or Picture format, whatever). I go to Folder Option and choose to remember the Thumbnails view for this folder and all subfolders. So far, so good. Now I choose the List view and only choose to remember it for the current folder. However, when I go into any subfolder, I get the List view in all of them. How can I resolve the situation without manually setting each and every subfolder's view?
Save a List view format for the parent folder, as you would normally.
For the other folders, go to Preferences / Folders / Folder Formats and add a new Wildcard Path Format. Set it to C:\The\Parent\Folder* and to use Thumbnails mode.
Thanks, got it to work, though saving List view still broke it, so I only created a custom wildcard format. Kinda unwieldy, but still DOpus is one of the only two file managers (out of a dozen I've tried) which has this functionality at all. 
What was causing this behaviour? Does saving a custom view for an individual folder somehow override previous settings for saved views for 'this folder and all sub-folders'?
Yes, there is only one format saved for the folder in question. Those formats have an option to also apply them to all sub-folders, which is the only difference between the two choices. Saving a new format for a folder replaces the existing one for that folder (if any).
Ah, I see. I hoped that each subfolder would get its own stored view, but apparently that is not the case. 
Just don't use the "all sub-folders" option when saving. Then it will only be for the specific folder. Sub-folders will then whatever other (default) format - or you can explicitly save formats for the subfolders as well.