Why does the kernel quit if I want to use minus a sum that I converted from a list?

Using Mathematica 11 when I define a list

yy = {x*43, 32*y};


and then convert it to a sum

yy[[0]] = Plus;
yy


I get, as expected, x*43 + 32*y.

However, as soon as I try to multiply my sum with a minus sign, i.e. when I execute

-yy


my kernel quits without any error message.

Any ideas why this happens and how to avoid it?

The problem can be avoided by converting the list using a Do loop:

sum = 0;
Do[
sum = sum + yy[[i]],
{i, Length[yy]}
];
sum
-sum
(* 43 x + 32 y *)
(* -43 x - 32 y *)

• I can reproduce it on Win10 V10.4 - V11.3 – Kuba May 8 '18 at 9:22
• Same on win7 64 bit. – b.gates.you.know.what May 8 '18 at 9:23
• p.s. Tr or Total or Plus @@ are more idiomatic than Do. And all work. – Kuba May 8 '18 at 10:29
• Reproduced for V11.0.1 and V11.3 on macOS. Voting for bug tag. – Henrik Schumacher May 8 '18 at 10:38
• Surely one of the weirdest bugs I've seen. -2 yy works just fine. -2 yy/2 crashes the kernel again, and so does I I yy. – AccidentalFourierTransform May 8 '18 at 13:36