I’ve just noticed with 18.08.14 that when I start a new project and decide to change the video mode from let’s say Automatic to whatever other setting in video mode (and vice versa) before importing the media, Shotcut will not recognize it. I know this because the Resolution, Aspect Ratio and FPS doesn’t change in the Export menu. I have to close Shotcut and reopen it for it to recognize the change in video mode.
I tested this with a Portrait-oriented video (shudder) and my results are that going from a set Video Mode to Automatic seems to work fine, but having Video Mode set to Automatic, then changing to a specific 16x9 Video Mode (prior to importing media), then importing a 9x16 video, and adding it to the Timeline (not a necessary step but I tested it anyway), will result in a 9x16 Project Preview/Video Mode and export settings, without the black bars that would be expected from having a portrait-oriented clip in a landscape-oriented project.
Selecting the Video Mode a second time after importing a clip seems to fix this, without the need for restarting Shotcut.
I also tested this on previous versions 18.07.02 and 18.03.06 and changing video mode worked fine, it does appear to be an issue with 18.08.14. (I tried 18.08.01, but it crashed when I changed video modes.)
This is fixed for the next release v18.09.