Split time HUD element not matching actual lap time

Sorry if this has been asked and/ or answered before, but I couldn't find anything after doing a quick search.

Is there a reason why the following happens? I'll be doing time trials or track day (or really any mode now that I think of it), and the HUD element that shows your split time (the set of numbers that change between green or red depending on whether you're up or down on your best time) will say, for example, I'm up by 0.500s on my fastest lap just as I cross the line. But the time that's recorded is invariably slightly slower than whatever the HUD element shows. So instead of 0.500, the recorded lap time might only be 0.486s faster.

Why is this? It kinda drives me nuts, TBH. I remember this being a thing back in PC2 as well. Is it a quirk with the Madness Engine maybe? Am I just stupid (entirely possible) and have set some setting incorrectly?

 

It is known for a very long time, even when you start your lap the delta will always show you are about 0.050 up. Also timing seems to round numbers in a weird way in general, resulting in 70-80% of laptimes ending on a .xx9 or .xx0 which is especially annoying in offline qualifyings with AIs where you have the exact same time set by 2 or sometimes even 3 drivers and Time Trial leaderboards whery you can clearly see it.