Paragraph Returns in Posts Are Automatically Deleted

I have this crazy thing going on, where a paragraph return will completely disappear, shifting the following block of text back up to sit right behind the full-stop at the end of the preceding paragraph.

To demonstrate:

Here is my initial paragraph of text.
Here is my second paragraph of text.

After publishing my post, the two paragraphs will look like this:

Here is my initial paragraph of text.Here is my second paragraph of text.

This doesn’t happen with every paragraph – it’ll be select paragraphs, and I cannot see how WordPress is chosing which paragraphs to display in this way.

To resolve this, I edit the post, re-apply the paragraph return, and update. When then viewing the updated post, this issue is fixed. But then, I see further down the post, it’s done the same thing with another two different paragraphs.

So… I go back into edit-mode, and fix the second occurrence. After updating, I check the live post again, and this second occurrence is fixed too. But wait! The first occurrence is back again!! Huh?

…and I end up playing this ridiculous ping-pong with every post I write. It’s driving me insane!

I write in Visual mode, but am happy and capable-enough to write in HTML mode, but neither mode seem to make a difference, and when the issue does occur (I’d bank on it happening), switching to HTML mode reveals no weird code. It all looks clean to me.

I can’t be the only person suffering this.