I'm not able to reproduce the mismatch between preview and render. When I go to edit the question and paste the source of that revision, I get the same (undesirable) rendering in the preview. Are you sure the preview worked before?

## Diagnosis

The problem is that you used **two** *'s **outside** of math mode. The markdown processing (i.e. converting markdown to bold, italics, headings, etc.) happens first (server side if you're not using the preview), and then MathJax processing happens. Inside dollar signs, markdown explicitly avoids things it would normally process, on the assumption that stuff is meant for MathJax to consume. But outside of math mode (or raw code mode), the `*`

in `\eqref{*}`

looks like fair game. When you use two of them, the markdown processor happily converts them to `<em>`

and `</em>`

and then MathJax has no chance.

**Proposed solution 1:** Don't use markdown special characters in `\label{}`

. The label you use isn't visible anyway (only the tag is).

Note also that when all the the MathJax on the page is processed together (which doesn't happen in preview), repeated labels will cause "Label multiply defined" errors in MathJax, because MathJax don't know anything about the semantics of questions and answers ... it's just one big web page to it. However, the same **tag** being repeated is totally fine (albeit potentially confusing to the reader).

**Proposed solution 2:** Put your `\eqref{}`

in dollar signs so that the markdown processor ignores it.

## Demonstrations

Problem: (Note I'm using `_`

instead of `*`

to avoid global collision with the label in your question)

```
$$\begin{equation} A = B \tag{*}\label{_} \end{equation}$$
Look at equation \eqref{_}; isn't equation \eqref{_} awesome?
```

produces the following output:

$$\begin{equation} A = B \tag{*}\label{_} \end{equation}$$ Look
at equation \eqref{*}; isn't equation \eqref{*} awesome?

Solution 1:

```
$$\begin{equation} A = B \tag{*}\label{ast} \end{equation}$$
Look at equation \eqref{ast}; isn't equation \eqref{ast} awesome?
```

$$\begin{equation} A = B \tag{*}\label{ast} \end{equation}$$ Look
at equation \eqref{ast}; isn't equation \eqref{ast} awesome?

Solution 2: (Note I'm using `__`

instead of `_`

to avoid collision with the problem demonstration)

```
$$\begin{equation} A = B \tag{*}\label{__} \end{equation}$$
Look at equation $\eqref{__}$; isn't equation $\eqref{__}$ awesome?
```

$$\begin{equation} A = B \tag{*}\label{__} \end{equation}$$ Look
at equation $\eqref{__}$; isn't equation $\eqref{__}$ awesome?

Global collision example:

```
$$\begin{equation} A = B \tag{*}\label{*} \end{equation}$$
```

$$\begin{equation} A = B \tag{*}\label{*} \end{equation}$$

`*`

as a label", which will certainly mitigate the problem, but my point is more about the preview not matching the rendered post than working around this specific parsing issue. $\endgroup$