I have put together several test cases that seem to be giving me problems. I am using Wordpress 4.2.1 with a child theme based on WP's twentythirteen theme. The child them doesn't do much though, adds a few shortcodes and a few other minor changes..

I have also attached the HTML text of the page so that you can see the exact code and formatting that I'm using ... If you could help identify what's going on, that'd be great!
 

Test 1

[expand title="Normal formatting works fine" expanded="true"]

When everything is formatted "paragraph," there seem to be NO PROBLEMS.. yay!

[expandsub1 title="Even with nested expand elements"]They work great![/expandsub1]

[expandsub1 title="And another!"]Still working![/expandsub1]

[/expand]


Test 2

[expand title="Even when we bold, change color, etc. the body, everything works great..."]

This is paragraph-bold-blue text that should be hidden inside the expansion element. Works great. And below is an image that is properly hidden too!

sinewave_audiodane.gif

[/expand]


Test 3

[expand title="We can even bold a portion of the title and it works!"]

and the contents do still expand properly, yay!

[/expand]


Test 4

However, when we change color of a portion of the title, it does not work..

[expand title="However, when we change color of a portion of the title, it does not work"]

but the contents do still expand properly, so we have that in our favor!

[/expand]

Also trying to underline a portion of the title does not work..

[expand title="Also trying to underline a portion of the title does not work.."]

but the contents do still expand properly..

[/expand]


Test 5

[expand title="However, when we change color of the entire paragraph, it does work!"]

and of course the contents do still expand properly..

[/expand]


Test 6

[expand title="Now, if we try to have a title as one format (paragraph)"]

with a heading-6 body, it works!

[/expand]


Test 7

But if we try to have a title as a non-paragraph format (heading-6 for example)...

[expand title="Here is a heading-6 title"]

..with paragraph text that should be hidden but is not..

[/expand]


Test 8
[expand title="And here is a heading-6 title"]
..with heading-6 text that should be hidden but is not.. And it even changes the horizontal spacing of the text within the page for some reason.. ???
[/expand]