Shotcut "Behaves" Like working in 1080p even when working with 720p Footage

[shotcut]

There is no proof of a bug here. I think you are not using Video Mode correctly.

Video Mode

Introduction Video Mode is the project resolution, aspect ratio, frame rate, and color space. It is important to set this as you desire at the beginning of your project. If you try to change it later Shotcut will try to retain the timing of edits, but some users have reported problems, and it is risky. Also, at this time Shotcut will not automatically adjust anything for you related to size and positioning of elements like text and picture-in-picture when changing resolution. You can think of…

In particular read about Automatic. Even the text in the middle on the screen upon initial startup explains Automatic. If you want more predictability, then set Video Mode to something other than Automatic.