Hi Clive, Three observations about the clear LED cover that got the burnt spots – a) I think the manufacturer used polystyrene rather than polycarbonate for the shield, and it probably is not very flame retardant, maybe rated UL94 HB at best , where it should be UL94 V0 or 5VA rated material b) they placed the LED's far too close to the clear shield c) They may have been driving the LED's with way too much current. 10-15 mA is lots for LED's, usually.
If you cut away the burnt clear material over the LED's it will be an improvement on the flame retardency of the enclosure!
Chinese LED fixture makers get away with a lot. The better ones are fine, but there are some time bombs out there.
A UL or European agency approval sticker is a good thing to look for when buying an LED fixture but there are lots of fake stickers around, even ones with convincing hologram graphics that look real. If spending considerable money, I'd recommend calling the UL or Euro agency hot line and ask if the file number on the UL or agency sticker matches the product ID and serial number on the LED products. If they don't match, don't buy them. I've found some unsafe fakes that were on UL's black list by this method, on sale openly at a large hardware chain store here in Canada.