Ok, I found the answer, and now spoiler blocks (the ones using the following code) will collapse:
[spoiler=(Title text, similar format as the quote function, but without the quotes. Links do not seem to work.)]Line 1
Line 2
Line 3[/spoiler]
Line 1
Line 2
Line 3
Edit: The solution to get it working the first time was to clear the cache. The solution to get the collapse to work was to change var spoiler_collapse from FALSE to TRUE.