Describe the bug
If you upload an image to a block, change the size of it in Image Settings to e.g. Medium and then go to edit the image, after your edits the image reappears at Full size.

To Reproduce
Steps to reproduce the behavior:

1. Create an image block
2. Upload an image to the block. The image is inserted full size.
3. When the block is selected, in the sidebar Image Settings change the image size from Full to Medium.
4. Use the Edit image button to open the Select or Upload Media modal.
5. Add a caption and alt text to the image.
6. Press the Select button to update the image.
7. The image information has updated, but it has reverted to Full size.

Expected behavior
I expected that the caption and alt text would be added to the image but the image size would stay the same.

This happens also with images already in the Media Library, but it's more relevant with new uploads to Gutenberg posts because you cannot add the caption, alt text or description when you upload the image because the options aren't there.

Screenshots

Desktop (please complete the following information):

• OS: Windows 10 64-bit
• Browser: Firefox Quantum
• Version: 61.0.2
• Gutenberg 3.7.0