jj rebase --after does not maintain order of parents

[mlcui-corp]

Steps to Reproduce the Problem

$ jj
@    qont three (merge)
├─╮
│ ○  tpzo two
○ │  wouy one
├─╯
│ ○  vzkp four
├─╯

$ jj rebase -r v --after w
Rebased 1 commits onto destination
Rebased 1 descendant commits
Working copy now at: qont three (merge)
Parent commit      : tpzo two
Parent commit      : vzkp four

$ jj
@    qont three (merge)
├─╮
│ ○  vzkp four
│ ○  wouy one
○ │  tpzo two
├─╯

Expected Behavior

@ has parents four (vzkp), then two (tpzo).

Actual Behavior

@ has parents two (tpzo), then four (vzkp).

Specifications

• Version: f8e106a