You have this problem if the theme manager doesn't have an area about settings stylesheets. And you installed a fresh theme, otherwise, it takes from cache or site prefs. No idea, the old installation works.

Open theme.xml

<stylesheets>
<css file="style_default.css" name="Default Version" default="true" />
<css file="style_orange.css" name="Orange Version" />
<css file="style_green.css" name="Nightvision Version" />
</stylesheets> 

And add  to each line: scope="front,admin,wysiwyg"

Result:

<stylesheets>
<css file="style_default.css" name="Default Version" default="true" scope="front,admin,wysiwyg" />
<css file="style_orange.css" name="Orange Version" scope="front,admin,wysiwyg"/>
<css file="style_green.css" name="Nightvision Version" scope="front,admin,wysiwyg"/>
</stylesheets>

Then go to the Theme Manager and confirm that at least one of the styles is set as default. 

Confirmed:

Landing Zero 2 1.4	Fixed: LZ2 1.5