setSiblingIndex sets index to 0. bug?

Cocos Creator
#1

When SiblingIndex is busy, setSiblingIndex of another node may be set to 0.

Cocos Creator v2.1.0.

ProcA.ts

const {ccclass, property} = cc._decorator;

@ccclass
export default class ProcA extends cc.Component {
    private childNodes: cc.Node[] = [];

    protected start(): void {
        for (let i = 0; i < 50; ++i) {
            const newNode = new cc.Node();
            newNode.parent = this.node;
            this.childNodes.push(newNode);
        }
    }

    protected update(): void {
        this.childNodes.forEach(e => e.setSiblingIndex(0));
    }
}

ProcB.ts

const {ccclass, property} = cc._decorator;

@ccclass
export default class ProcB extends cc.Component {
    private siblingNode: cc.Node;

    private createSiblingNode(): cc.Node {
        const node = new cc.Node();
        node.parent = this.node.parent;
        return node;
    }

    protected update(dt): void {
        if (this.siblingNode) {
            cc.log(this.siblingNode.getSiblingIndex());
            this.siblingNode.destroy();
        }
        this.siblingNode = this.createSiblingNode();
        // The SiblingIndex set here is occasionally 0.
        this.siblingNode.setSiblingIndex(this.node.getSiblingIndex() + 1);
    }
}

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