Thank you for all the comments, guys. As usual, some sound sense and some nonsense.
The guard is made from, IIRC, PE. I can't remember if it is HDPE or LDPE, but most definitely not acrylic. It would not have survived if it was, it would have been in a million pieces. Mine covers the blade much better than the crown guard that came with it, which was small, impossible - and I do mean impossible - to adjust properly and could actually fall onto the blade. This one can't. It covers the blade at both sides completely, as well as above and is taller than the blade, so it hits the table before it can touch the blade. It's not flimsy at all, but the support arms were not designed to withstand sideways forces and that most definitely is a weakness that needs addressing.
I went down to have a look this morning and I now know what happened. It was as I suspected, the guard making contact with the blade. That is my fault, it was set in the wrong place relative to the saw slot. It's because I recently modified it to remove an annoying glitch. It doesn't matter when doing normal cutting, but when tilted, the blade is too close to the cover. I must have pushed the cover in slightly with my pushstick. The back rising teeth picked up the back of the cover so that the front was brought into contact with the teeth. The fact that it survived in one piece, albeit damaged, is testament to its robustness, I think. The swing arms are deliberate. They allow the cover to rise above the work as, and only as, the workpiece travels over the blade. It drops down at the front as soon as the wood goes past. It means that there is always something between me and the teeth. Always. It works superbly under normal circumstances.
I think the only flaw was the positioning of it. I might make the swing arms out of steel rather than wood and I need to beef up the fixing points of the fence shoe support, but otherwise I shall rebuild it just as it was. Except for its lateral positioning, of course.
I'm really rather pleased that I now understand what was wrong, although I still don't know which bit of it hit me, the guard or the pushstick.
BTW, Bob, I was using a short fence and the blade was sharp (at least, I hadn't had any other indications to the contrary - although it isn't any more...). And my point about putting the fence on the left is for bevel cuts on right-tilt saws - only for that - so that neither the workpiece nor the off-rip get trapped between the underside of the blade and the fence.
So I shall put it all right tomorrow. I do have a spare blade (yes, it is a Freud), so I can carry on, but all my other blades, half a dozen or so, have gone, including a rather nice DW crosscut blade and a FTG one that was perfect for splining mitres. So I shall have to either buy a replacement (not available in the UK AFAIAA) or see if the saw doctor can bring it back to life. It's not seen a great deal of use and I do like it. Unfortunately, the saw doctor is a much greater distance away than he used to be, and I went only last week.
Two other points:
1. SUVA means something in Swiss:
http://www.suva.ch/english/
It's the initials of an insurance company. The style of guard is one they are happy to insure against, so they, at least think the design is not fatally flawed.
2. My finger is fine today, thank you. The nail is a bit tender if I press it, but it's not needed a dressing, let alone troubling the busy people at A&E. It's just a bit bruised and scraped. Actually one of the other abrasions has given me more trouble today than the nail. It's just on the inside of my finger, so I catch it every time I pick something up.
I've learned something from this, and if it has helped anyone else then, well, I won't say that it has been worth it, but every cloud, eh?
Jacob, you can buy me a commiseration pint on Thursday.
PS Why are saw doctors called saw doctors? They deal with teeth, they should surely be saw dentists ???