Hi there @dale! Thanks for bringing this up! This is actually the same behavior discussed in this earlier thread.
At the moment, locking proportions doesn’t fully prevent changes when elements are inside a Stack. The Stack’s own resizing rules can override the lock, which is why it may feel like the proportion lock isn’t working as expected.
The team is aware of this, and we’ve shared the feedback internally so they can review how proportion locking should behave within Stacks. While I can’t promise a timeline, your report helps us keep improving this feature. Thank you for taking the time to share it!
Tip in the meantime: If you need to resize the image while keeping its proportions, try using Scale (⌘K) instead. This ensures the aspect ratio stays intact regardless of the stack’s constraints.