Dell Venue 8, Windows 10: Handwriting panel not working after upgrade to build 1511

I have a Dell Venue 8 tablet, which I've always been pleased with.  Along with my principal desktop and laptop, I upgraded from W8.1 to Windows 10 entirely successfully.  More recently, I've upgraded (via Windows Update) to build 1511.

Now the handrwriting panel (which I've always used with the Dell stylus, or simply a finger) is unavailable.  If I open the on-screen keyboard, and tap the keyboard selector icon, I'm offered the standard keyboard, the split ("thumbs") keboard - then the pen/tablet icon greyed out and inactive - and finally the full keyboard.

This all worked right up until the time of the upgrade to 1511 (although I can't be entirely certain that the upgrade caused the problem).

I can't get any help at all.  I tried Windows Answers, but (as usual) wasted many minutes in superficial chat with what I'd guess was an intern out of his/her depth, and who finally referred me to Dell.  I spent ages going round in circles trying to get into my Dell community account and ended up having to create a new one this afternoon.  In the past I've used Usenet, but while there are a few pockets of expertise remaining there, but not, it seems, anyone with W10 knowledge.  Of course I've tried the usual search engines, but all pull up a variety of articles for every version of Windows except W10 - whatever search terms I use.

Can anyone help? Even just by identifying the relevant service or other facility that I can try twiddling with?  (Of course I've twiddled with, and Googled, the Touch Keyboard and Handwriting Panel Service without any luck.)  Is it me, or is Windows becoming less and less transparent, meaning that when something stops working you're simply stuck?

Phil, London