There seems to be a problem with blockquoted spoilers that contain code blocks. You can see an example in this answer. Here's how it shows in my browser (Chrome 43):
You can clearly see the text even though it is supposed to be a spoiler.
Sometimes, answers require a visual text representation, and the code formatting works best because it is the only way to force a monospaced font.
This also only seems to be a problem on the puzzling.so site, and not on meta or other SO sites.
Please fix the CSS to accurately retain the spoilers.