Wow, really odd problem!

Two clips directly from a DSLR on a DSLR 1080p timeline.

Additive Dissolve, Dip to Black or White work perfectly

Cross Dissolve however changes aspect ratio during the dissolve! What am I missing?

The frame before the is 16x9, the cross dissolve squashes the footage vertically then the next frame after the dissolve is fine (16x9). What could I possibly have done wrong?

Even with more info I'm not sure we can help but definitely can't witihout knowing more particulars. Your DVinfo profile still indicates you use FCP7. What version of PPro are you running (including patches; current is 5.03), and on what hardware? PC or Mac, processor, RAM, GPU?

Thanks. I updated the profile.

CS5, purchased via downloaded only a few days ago, so I assume it's the latest.

MacPro 8 core 16GB RAM.

It's really odd. If I select the Cross Dissolve then in the effects tab move the dissolve a couple of frames left or right, then put it back where it was, it's fine. If I don't drag it it's not. Weird. Any ideas?

If you downloaded the main software and didn't do any patches, you probably have the release (5.00) version; you should be able to go to Help >>About to confirm the version (I'm on PC so maybe the menus structure is a little different on Mac). Go to Help >>Update and prepare for another huge, but simple download to the latest version.

If the problem still persists after verifying that 5.03 is loaded and otherwise running, post again and let's see if someone can figure it out. If not, then the next step is bug reporting to Adobe.

The only culprit i could see (off the top of my head), is
A) Sequence settings not matching the footage dimensions, or
B)Not enough tail/head frames to do the cross dissolve..

Thanks for the replies guys.

I've double checked the sequence settings - it matches the clips.

Lots of handles, no problems there at all.

And as I said above, it I move the position of the cross fade by just one frame in the effects table then it's the right size and renders perfectly.

Maybe I should put a video together showing it so you guys can tell me which 'stupid' hat to wear because I'm not doing something right?

Frankly, I don't mind if I look stupid provided I can find the cause and fix it!

Make sure 5.0.3 is installed. It fixed a lot of issues.
If you are one MPE hardware, does the issue still occure when turned to MPE software?

5.0.3 is installed.

MPE is software only (ATI card installed).

is the footage being interpeted correctly ? in the project window it should show 1920X1080 @ whatever FPS

if its some how set to 1440, that could possibly cause the problem.

also are you on OS 10.6.4 or newer ? if not that would be the very next thing to update to 10.6.5 or 10.6.6

There're lots of people with this type of problem. I didn't pay much attention to it until I encounterd a same problem. In my case as well as many others, unchecking "use max. render quality" box solved the problem. Give it a try and let me know if it worked or not.