This is the weirdest thing. I tried to reproduce the bug (with 3837 Tier 2 Feedstock as you have), but for me as soon as I type the second 8 in the copper box, it actually does add up to 379,09,56. But on this server, the minimum price right now is actually 9,00 not 9,88.
That total price is as if you had entered 00,09,08 instead of 00,09,88. So far, I'm not sure how to reproduce the error. What language of keyboard are you using, by chance?
I found a way to reproduce this bug but I don't know if it's the same issue:
1. Put in something to sell.
2. Randomly spam numbers and the backspace key. :D (I didn't do this for the actual bug. Just tested it because it came to my mind)
3. One number you typed (let's say the number 1) will bug out:
-> You have nothing ("") in your field and type this number it won't change the total asking price.
-> You have a number which contains this number in your field ("x1"). The total asking price won't change if you delete the other number ("x")
I don't know if this is leading in the right direction and is an issue for the bug I found but maybe you have got an idea.
I can provide screenshots how to reproduce this, if it's too difficult to understand.
@counterpoint: I am using a German keyboard.