Link to load lightbox doesn't cover image if text wraps

When I hover over an image, the link to load the lightbox only displays over part of the image.

This occurs if the image is aligned to the right, and the text wrapping to the left is in a <blockquote> or a <h1> – but not a <p> so I’m guessing this is caused by a blocking element. The part of the image that is on the same lines of text as the blockquote/h1 has no clickable link, however if I move the mouse upwards to a part of the image where the text is not to the left, the link is suddenly active.

I’ve used the “Add Media” link and so the shortcode/html is something like:

[caption id="attachment_327" align="alignright" width="213"]<a href="http://mysite/image.png"><img class="size-medium wp-image-327" src="http://mysite/image-213x300.png" alt="description" width="213" height="300" /></a> some caption[/caption]

at the top of the page, the next line is a h1 tag and where the image floats to the right with the h1 text wrapping to the left, the part of the image horizontally to the right has no clickable link. If I keep the mouse on the image and move it so it’s underneath where the h1 ends, the link suddenly appears as clickable to load the lightbox.

https://wordpress.org/plugins/wp-jquery-lightbox/