Spoiler markup does not break line for series of MathJax equations in post previews

Question

Putting a spoiler on MathJax equations does not work well sometimes, as reported here (1st answer).

For example,

$$a=1$$ $$b=2$$ $$c=3$$

can be written using

> $$a=1$$
> $$b=2$$
> $$c=3$$

or

> $$a=1$$ $$b=2$$ $$c=3$$

However, writing

>! $$a=1$$ $$b=2$$ $$c=3$$

or

>! $$a=1$$
>! $$b=2$$
>! $$c=3$$

results in no line breaks in the preview pane. To see this in action, edit this post and look at this block:

$$a=1$$ $$b=2$$ $$c=3$$

Where have the line breaks gone?

Answer 1

More tests

Test 1, quoted:

$$ \text{ this line is centered and the fraction is } \frac{full}{size} $$

>  $$ \text{ this line is centered and the fraction is } \frac{full}{size} $$

spoilered:

$$ \text{ in preview, this line is not centered and the fraction has } \frac{reduced}{size} $$

>! $$ \text{ in preview, this line is not centered and the fraction has } \frac{reduced}{size} $$

Test 2, quoted:

$$ \text{ this is \$\$-delimited } \\ \text{ and has multiple lines } $$

>  $$ \text{ this is \$\$-delimited } \\
      \text{ and has multiple lines }
   $$

spoiler attempt:

! $$ \text{ this is \$\$-delimited and has multiple lines } \\ \text{ but the exclamation ! point isn't parsed } $$

>! $$ \text{ this is \$\$-delimited and has multiple lines } \\
      \text{ but the exclamation ! point isn't parsed }
   $$

compulsively-formatted quote attempt:

$$ \text{ this is \$\$-delimited and has multiple lines } \\ > \text{ but only the first right > broket is parsed } > $$

>  $$ \text{ this is \$\$-delimited and has multiple lines } \\
>     \text{ but only the first right > broket is parsed }
>  $$

Test 3, quoted:

\begin{matrix} \text{ this uses \\begin\{matrix\} without \$\$ } \\ \text{ and has multiple lines } \end{matrix}

>  \begin{matrix} \text{ this uses \\begin\{matrix\} without \$\$ } \\
                  \text{ and has multiple lines }
   \end{matrix}

spoiler attempt:

! \begin{matrix} \text{ this uses \\begin\{matrix\} and has multiple lines } \\ \text{ but the exclamation ! point isn't parsed } \end{matrix}

>! \begin{matrix} \text{ this uses \\begin\{matrix\} and has multiple lines } \\
                  \text{ but the exclamation ! point isn't parsed }
   \end{matrix}

Answer 2

Check out my answer for:

All neighbor sum is 0 on a chessboard

to see how to spoiler long MathJax.