If I were in that spot, and was just looking for workarounds vs. solutions so I could get the job done and fix it later, I would try putting the offending images on their own track to see if it helps not having them directly fade into another image by overlapping on the same track. If that didn't help, I would try to use the composite level rubber band (right click on the clip, and select composite under envelopes) and see if making the fades that way still produces the same unwanted side effects. In my 15 years with Vegas, I've found if a fade gets buggy for whatever reason using the normal route (such as when you fade into a clip that has the color match plugin on it and you are using GPU acceleration), you can get around it by using the composite level rubber bands (or by disabling GPU acceleration, another thing you could try). You mentioned having to fill in the blank spaces with black to prevent the shine-through, so maybe another alternative would be to fill in that space with a solid color generator on a track beneath the image that is all black.

Hopefully one of those helps you get things done until we can figure out what is causing this.

Thanks for the suggestions. Off to "the big city" (Cartagena) this morning so will look at this later and get back. Thanks again.

To be clear, did you apply a Transition / Dissolve or the Automatic Crossfade that comes from overlapping the media on the timeline? Example:

"I have had to import the portrait image into an image editor to place it within a 4:3 frame with the blank filled with black, which is a bit of a pain!"

You don't need to use an image editor for that task.

1) Just put the cursor over a portion of the image that's not involved in the dissolve or crossfade

2) Press the Diskette icon button over the Preview, "Save snapshot to file":

3) Replace the 4x3 image with the newly saved image. It will have black on both sides. The aspect ratio will match your Project Properties. 

Just to illuminate the problem, which was difficult to put into words. Here's the screengrab of the timeline. Yes the images overlap as per Automatic crossfade, so I drag the whole bunch of images to the timeline and they overlap as per this setting.



Here is the timeline with the "landscape" image the first event, and portrait image the second

And the resulting preview (which also renders as this)

I'm about to try the suggestions above and will report back!

Looks like you have two images in the same location. Delete one of them & see if the other one is "under" it.

OK. If I put the portrait image on a different track and drag the fades manually, the dissolve occurs, but at the end of the fade, the first, landscape image pops up again behind the portrait image! (Yes, I am using GPU acceleration but no plugins).

When I right click on the clip, I'm not seeing anything about composite envelopes.

I've tried solid black event on a track below, in different combinations (on it's own, fading with the first image etc etc) but it flickers on and off during the dissolve.

I don't believe it! I tried the suggestion to save the snapshot to file and now get the FOLLOWING image appearing behind the portrait one.

Turn off GPU acceleration... still the same!

I will not be beaten.......

Here's what's happening now. All 3 images (the two landscapes either side plus the offending portrait) now on timeline having been saved as snapshot files. The cursor is right in the middle of the portrait image, away from the fades, and this is the preview (the following image now showing beneath).

Looks like you have two images in the same location. Delete one of them & see if the other one is "under" it.

No, nothing else there! Hangon, sorry. One of my snapshot files contains both images! Eek. Sorry. trying again.

Yes! By saving the 3 images as snapshot jpg files, that has worked. Thank you. And with GPU acceleration back on too. All I have to do now is remember to do this each time I have a portrait orientation still image on the timeline.

Thank you for all the help!

I've found a better way to fix this, as the problem just "cropped up" again! Dissolving one portrait jpg image to and from two landscape jpg images. On the portrait image, I went into Event pan/Crop, applied Preset "16:9 Widescreen TV aspect ratio" then stretched it so the image was full size within the mask. No fade problems! Done.