Comment 1 for bug 1672269

Predictably it seems r4035 caused this. Although curiously there is only a problem if you rotate before changing modes and not vice-versa...

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revno: 4035 [merge]
author: Daniel van Vugt <email address hidden>
committer: Tarmac
branch nick: development-branch
timestamp: Thu 2017-02-16 04:47:36 +0000
message:
  Add letterboxing/black bars support to the GL renderer, for when
  the logical viewport aspect doesn't match that of the screen.

  This will be used in future for arbitrary cloning of one monitor
  to another (LP: #1639226)
  . Fixes: https://bugs.launchpad.net/bugs/1639226.

  Approved by Brandon Schaefer, mir-ci-bot.
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