Why can't the HTML remain on a truncated post?
If remain the HTML from the content then it will caused truncation will not show accurate the character, because it will count HTML tag as well.
Since you would like to show truncation from your blog listing page, I would like suggest you to use `Read more` block, you can refer on my attached screenshot below. (I already help you added read more block from this post `October Speaker`)
Hope this will help.
Plus, the image itself is showing a caption when I've changed the type of image from captioned to Polaroid. It hasn't changed no matter how many times I've cleared the cache it still shows the caption.
It would be best if you can start a new thread with this new question, so that our multiple moderator will easy to manage with your issue.
And elaborate more details regarding this issue. For example : which post and which image caption you referring.