"Long Lived" trait acts strangely

[SassisSass]

I've been wondering for a long time why sims with "long lived" trait just won't die and we end up with big families of old people, basically a retirement home. I've searched through many forums and no-one seems to have an answer to that. Recently I finally decided to delve into the world of mods to combat many annoyances this game has to "offer". So thanks to all the cheats and data the famous MCCC offers I decided to examine this trait.

First, already known facts. If we take normal lifespan as a basis then every life stage in short lifespan is half of that of normal and long is 4 times longer than normal. Now, base number of days elders live is 10. It can be a day or two more or less, depending on sim. "Long lived" trait gives extra 17.5 days according to sim stats in MCCC, showing "Days Left (28 including 17.5 Bonus Days)" (the game seems to round numbers up to integers). The base number of days given to elders in long lifespan is 40 (4 * 10). However, if a sim gets "long lived" trait, the MCCC reads: "Days Left (320 including 70 Bonus Days)". As you can see, the bonus days are also 4 times more (4 * 17.5 = 70) but actually the bonus days are multiplied by 4 twice and the real calculation is 40 + ((17.5 * 4) * 4) = 320. I looked at many sims and this calculation holds even when a sim would be given more or less days to live. For example, if in long lifespan and elder has 37 days to live then with "long lived" trait it would be 37 + ((17.5 * 4) * 4) = 317 days.
A similar thing happens with short lifespan, only there bonus days are divided by 2 twice i.e. 5 + ((17.5 / 2) / 2) =  9.375 ≈ 10 days. The MCCC would again read "Days Left (10 Including 8.75 Bonus Days)". 
I find it really strange. This trait should follow the same rule by giving 4 times more bonus days in long lifespan than normal and 2 times less in short but the multiplication and division are done twice for some reason. What do you think about it?

P.S. Fun fact: "Long Lived" trait is linked to base elder days i.e. it's 1.75 x 10 = 17.5. So, If you use mods and change elder's lifespan to something else than 10 then the bonus days also change.