I'm still new to all this, so any oddness is probably my fault! BUT - here's a possibility - when I tried to buy the photo matte paper direct from HP, they told me they had none in stock and thought that it may be being discontinued. As I say, I'm using CS3 and therefore no plug-in, and the machine's only about a month old. Perhaps they pulled the profile from software that's not using the plug-in? (But that would require HP to be incredibly efficient...)
Anyway, I'll get on with checking the links you posted in case my theory is wrong! - thanks.
EDIT: OK, the difference is that I have been letting PS manage the colours. When I let the printer manage the colours, I get the Photo Matte option, exactly as you say, and as reproduced in the first link. And this is what I had when, in PS7, I used the plug-in. Thank you!
It is odd, though, that when PS manages the colours I don't get the profile. I watched the Radiant Vista tutorial on this and it said that if you want correct reproduction, PS should manage colour. - any thoughts?
In the meantime, perhaps we've resolved the issue of the head-strikes!