This is a problem if I export the video. As I know Preview Scaling is only for "Preview"ing the export. I want to turn off the Preview Scaling when exporting. However it results that my Zoom filter is not applied when exporting.
Why are there two filters Size, Position and Rotate on the same clip?
Another interesting point you should know is that the order of certain filters is important and influences the final result.
The preview scaling has no influence on the exported video because by default the export is done at the same resolution as the project was set to (for example 1920 x 1080 30 FPS). (The scaled rendering checkbox on export is disabled by default)
If you use the automatic mode when creating a project, you should know that the first video or image file will be used by Shotcut to determine a project resolution according to this file.
This is not a bug with preview scaling; it is a bug when not using preview scaling and multiple Size, Position & Rotate filters. I reproduced it. To workaround it, you should change it to have one filter and keyframe both things that you need.