Latest Update 4.15.0 has some problems - Buttons field, maybe more

Initially when i tried the update, it returned an error saying the update had not completed successfully, however the version number has updated.

The I noticed that the buttons fields were all broken.

The buttons now render as:

<i class="dashicons dashicons-images-alt2"></i> Add Image

If I look at the source then it seems that the html opening and closing tags are being sanitized.

<i class="dashicons dashicons-images-alt2"></i> Add Image

I have not checked too deeply in other places, but this is quite irritating. Do you know what has gone wrong?

Thanks

Guy