I'm not sure if we can fix this, but I did some testing and suspect it happens only when there are ' and " in the spoiler title. Eg:
[spoiler=Doesn't work]Nope[/spoiler]
These two characters mark beginnings and ends of strings (variables for storing text) in computer code and when the program encounters them, it may think that a string has ended there and messes up. If you cannot avoid these characters in spoiler titles, write a \ before the ' or ". This tells the little buggy piece of code that that ' or " is just a piece of text, not the end of a string, and it should go on.
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Example:
[spoiler=Don\'t test, does work]Hey, this works![/spoiler]
Spoiler: Doesn't work show Spoiler: Don\'t test, does work show Edit: I tested more, the problem seems to be in the expand/collapse code of spoilers, we'll see if we can do something with it.