Unpredictable behaviour?

[rhebus]

I find there are a number of aspects of the game's behaviour which just don't seem predictable and it makes life incredibly frustrating in time-trials. There are a number of places where there's a really fast line but it seems like the game only allows it half the time -- so either I take the risk and lose most of my attempts to (seemingly) arbitrary failure, or I don't take the risk and get a worse time.

Here are some specific examples:

* 9 o'clock news: sometimes you can walk straight off and through the first gap in Vertigo, sometimes you just don't make it and die instead. It might be something to do with the speed you've reached before you walk off the ledge, since if you get a bigger runup you're more likely to make it, but it's not a simple relationship.
* From In the margins to final challenge: sometimes you can walk straight out and miss the spikes on the first ledge. This *doesn't* seem to be a speed thing; in fact, the further you are from the edge when you start walking, the more likely you are to hit the spikes.
* Three's company: sometimes you go further through the first rubber band than you expect, causing you to overshoot your jump.
* Then there's Souleye's description of a similar problem in I'm Sorry.

Does anyone have any idea why these strange behaviours exist? Is the game nondeterministic, or is there some other explanation? 

[The Brass]

I have no idea and Three's Company is still one of the hardest rooms for me, but for 9 o'Clock News, start by bouncing downwards from the left prong of the M tunnel and you'll get the extra vertical clearance you need.