color cast caused by IR contamination? so how?

I just ordered my big stopper online, was contemplating on hitech's nd3.0 but so many reviews showed the magenta cast and the difficulty in removing in PP. Even the Lee's have a blue cast but deem to be easier to remove or correct in PP.

Searched far and wide (on the internet) for the cause of it, was "told" its because of Infra-red contamination. Simply put, too much infra-red affected the color of the image. Most camera have a IR-cut filter attached to the sensor which blocks out quite a bit of IR (but not all), but when long exposure is needed, quite a fair bit of IR actually penetrates to the sensor thus the color cast. The easier way to correct the color cast is by correcting the white balance. Or logically, we can try to reduce IR by adding a IR-cut filter but I discovered they are so rare and expensive it doesnt seem logically at all!

Here are some confusions that I have.
1) if color cast is caused by IR contamination why aren't the filter makers blocking the IR in their ND filters?
2) If color cast is caused by IR contamination, why does color cast seems most obvious around corners? or does it?
3) Light leakages cause color cast as well?
4) IR-cut filters, worth it? I can only find B+W, any other brand makes it?
5) Why the different color cast? IR seems to be in the red side of the spectrum right? so shouldnt the cast be red? instead of blue in Lee and magenta in Hitech?

Anyone can help?

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