Created attachment 166072 [details]
A photo of the preview of the output, showing the transformed and blurred background

SUMMARY
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I wanted to make a horizontal video vertical using a blurred background, so I created a vertical clip and imported my horizontal video. Kdenlive automatically made it fill the horizontal space, leaving black space both above and below. I then duplicated the clip and blurred the version below, then added a transform to scale to 320% size so the blur filled the background of the frame. (See the attached image). 

In the preview it looks perfect, but upon attempting to export, I noticed the blurred background was not present at all, it was just black. After removing the unblurred version of the video, i found that the video had infact been blurred, but that the transform was not applied to the final render.
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STEPS TO REPRODUCE
1. Import a horizontal video to a vertical project
2. transform that video by scaling it up to 300% so that it fills the frame
3. Render the video and discover that the the transform has not been applied.

OBSERVED RESULT
The render does not apply the transform, hence the output does not look like the preview

EXPECTED RESULT
The render should apply the transform, so the output is identical to what is shown in the preview

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma:  Fedora Silverblue 39
(available in About System)
KDE Plasma Version: n/a
KDE Frameworks Version: 5.115.0
Qt Version: Version 5.15.10 (built against 5.15.10)
Kdenlive version: Version 23.08.4, installed from Flathub
MLT Version:  7.23.0 
Windowing system: Wayland
GPU: AMD APU Ryzen™ 7 5800U with Radeon™ Graphics × 16