And as for this layout engines business...
Yes, IE Mobile has never used either the Tasman engine, nor the Trident engines (the ones used by IE Windows and IE Mac, respectively). Instead, it has employed that weird 'thing' they developed in-house in Windows Mobile division.
Now, the Weird Thing has never really got page rendering particularly right - and doesn't seem to be doing so, now. Compare the Trident VI engine (from recent builds of IE 8), rendering the Acid 2 test (which it passes perfectly, of course), to the odd assemblage of coloured lego bricks, delivered by IE 6 Mobile against the same test.
Are these products even being made by the same company?
And therein lies part of the problem, because, when presented with conditional comments that stipulate "If IE 6" (to include correctional styling rules for IE6/Trident desktop version), the Weird Thing on 6.5 Mobile will now attempt to import and apply those rules as well! This means that web developers are robbed of one of their main tools in correcting rendering errors in IE6/Trident, because the Weird Thing will think the developer is talking to it, too.
(Many web developers will, at this point, no doubt be hoping that Windows Mobile's market share remains at its current 'robust' levels of growth... that way, they may never have to worry about any of this crap.)
You see, the version of IE being shipped in WM 6.5 is actually a rush job, originally intended for the Chinese market. It has been included in 6.5 because a revised rendering engine is still causing handset crashes. Why can't they port Tasman or Trident to Windows Mobile, you may ask (other than selfish pride, hubris, and a desire to "get one back at The Man", over in Windows main division)? It surely can't be beyond the wit of even those guys in Mobile, to do so? After all, Operasoft have ported their 'Presto' engine to just about anything with a screen on it - and when you talk to Presto, you more or less know what to expect from it!