When you put certain types of VB code in it:
Coloured text shows,
but bold, or
or a font change are hidden.
But a smilie is not!
It shouldn’t work that way, right???
Not an expert, but taking a guess.
The blackout works using a standard system of turning the background in the window to black. When the text is also black, there is no contrast and thus the text is obscured. Using color creates the visual contrast, just like you programmed a web page with a black background and colored font as your motif. Ergo, it is working correctly, just not ideally for a true spoiler prevention. That’s the way html coding works, so you just have to work with it.
Smiley’s are the same thing. The gif inserts, and the color contrasts with the background. Ergo, smileys show up.
The spoilers tag was basically vB trying to add a useful feature without bloating the software too much, I presume. Either way, basic HTML presents a convenient solution that works most of the time (especially on a black-text board like this). So what the hell, might as well use the easy way.
Just hope raisinbread doesn’t discuss next week’s 24 or there’ll be hell to pay. 
I believe that the spoiler tag is a customization added by our own staff, and they don’t have the option to bloat the software at all. Adding simple tags is something the administrators can do, but any changes to the underlying code would void the service agreement.
Didn’t it originate as an option on that other board during the Winter of Our Missed Content?
When it’s mounted on a Saturn?
Another thing I noticed quite by accident:
When you search for a word, and it appears within a spoiler, it will become visible, since the words searched for are highlighted by changing their color.
Yeah, I think so. the BB board had the option, and we pounced.
And Chronos, I stand corrected.