No, that's not it. I'm familiar with the effect you're describing, and although I agree that it's probably a tad too strong in T.S., it's not what I'm referring to.
A simple example of a place where it happens and definitely has nothing to do with the edges of the platform is Speedbumps Road 1, the first sequence.
You start by taking two straight jumps over the first two hurdles, as you accelerate. At this point you are probably dead in the center of the platform, and want to make a lateral jump onto a side platform. If you are going full speed, you will need to start this jump while still in the middle of the bounce after the previous jump. And precisely at this point I often see that the arrow key did not register, and my third jump is going straight.
After noticing this, I went back and did a little more research of the phenomenon, and looks like the problem of the direction keys not registering only happens if you are trying to do consecutive jumps, that is going from a bounce into your next jump. To check this I took an easy road that starts with a long stretch with no obstacles (Read Heat Road 1). I start by accelerating, and then jumping sideways at some point. I noticed that no matter when or which direction I take my first jump, and when - it always registers fine. But in the previous example (Speedbumps), because my jump follows the bounce of an earlier jump, it often does not register the side key.
So it looks to me like there may be some subtle timing issue during the short period of the bounce, where the game will fail to register an arrow key (but will register the jump key itself just fine!). The solution I found that almost always works is just to press the arrow key harder and for a bit longer. It is also less likely if you hold the space bar down between the jumps instead of tapping it (but it is a bit difficult for me, because it goes against my style of play).
I imagine that the reason why you are not hitting this problem is because you either push the keys harder/longer by default (my style is fairly light keypresses), or because, as you mentioned in the other thread, you do tend to hold the spacebar down for consecutive jumps, whereas I mostly tap.