yeah thats right the central column is not revealing as per the expected response as seen on youtube. this game needs serious patching.

I encountered that the first time around (but found a way to hurt it anyway, and almost beat it that time), and it DID open up the second time around.

If it doesn't open as shown in the video, just jump up on the sucker - you'll sort of find yourself inside the thing - and start blasting away.

yes that ended up working for me, unfortunately it doesn't work for all enemies. The dual purple plasma ball one got stuck in the roof and there is no 'fly' power up nor 'ghost' power up enough to fix this games glitchyness.
And that isn't the only boss glitch as I've found such occurences happen to most of the bosses and with a frequency that is unacceptable.
As far as I'm concerned this game is broken. why play through levels to get to the second last level and hit a road block of an invincible boss just because the developer couldn't code properly.

Not sure what to tell you. I've seen that one particular boss bug Scrambler) only the first time around, and then had some clipping at the Sanctum boss fight - but eventually popped back into the 'arena' within five or ten seconds and finished it off. My experience is that there are a couple parts that need some tweaking but that it does work all the way through. Obviously, you're getting a different result.