"abort: push creates new remote head A on branch 'B'" on push

Had seen this in the past for mozilla-beta (to whose fresh clone I never tried to push again), now it’s hitting me when I try to push to mozilla-aurora (never pushed to it before):
$ hg push pushing to ssh://hg.mozilla.org/releases/mozilla-aurora/ searching for changes abort: push creates new remote head 7cedfa46219c on branch 'CAL170_20121003_RELBRANCH'! (merge or see "hg help push" for details about pushing new heads)
My change was an uplift from mozilla-central. The tag seems to be from comm-aurora (or has it be pruned from mozilla-aurora?).

$ hg branches default 325508:8259dc6e226e

`$ hg log
changeset: 325508:8259dc6e226e
tag: tip
user: Gregory Szorc
date: Mon Jul 18 10:24:27 2016 -0700
summary: Bug 1287439 - Update robustcheckout extension with upstream; r=Callek; a=sledru

changeset: 325507:661d3548825a
user: Nicholas Nethercote
date: Thu Jul 21 08:13:17 2016 +1000
summary: Bug 1262731 - Don’t use a separate ICU data file on Windows. r=ted, a=gchang`

hg heads shows only one head:
$ hg heads changeset: 325508:8259dc6e226e tag: tip user: Gregory Szorc date: Mon Jul 18 10:24:27 2016 -0700 summary: Bug 1287439 - Update robustcheckout extension with upstream; r=Callek; a=sledru

Any ideas what’s wrong and how to fix it?