We've had periodic reports of trouble with annotations changing unexpectedly, and we are pretty sure we have a reproduction of the issue and and explanation. A workaround, too!
If you make a change to the annotations and press Enter, you will notice a green pencil icon to the left of the field that you changed. This indicates that you have unsaved changes:
If you then select several images in addition to the one you have been working on, you will inadvertently replicate the unsaved annotations on all selected images to the same values. This is a bad thing.
We've asked the development team to change this behavior, but in the meantime, there is a very simple workaround:
Hope this helps!