Changes have been made in Git (master):

commit 2f0d4b2305fb54c4405a202d1adcf9284c5b4a67
Author: Michael M Slusarz <slusarz@horde.org>
Date:   Fri Mar 23 13:34:08 2012 -0600

     Bug #11099: Move popup js inclusion into Horde_PageOutput

  framework/Core/lib/Horde.php              |    2 +-
  framework/Core/lib/Horde/PageOutput.php   |   13 +++++++++++++
  framework/Core/lib/Horde/Script/Files.php |   28 ++++++++++++++++++++--------
  3 files changed, 34 insertions(+), 9 deletions(-)

http://git.horde.org/horde-git/-/commit/2f0d4b2305fb54c4405a202d1adcf9284c5b4a67

Then it was because of this failed conversion when converting to 
Horde_PageOutput:

array('onload' => 'dom')

'onload' is now a boolean value.  And intval('dom') === 0.

The problem was that it was *not* wrapped in a dom:loaded event if 
called when output already started, even though it was supposed to.
This has been fixed with some of recent commits, it's properly wrapped 
again now.

And that's the expected behavior, right?  It is wrapped in a 
dom:loaded event, and is not attempted to be inserted into the Horde 
object until the page is loaded, since there is a chance that the 
Horde object won't be loaded until later in the page?

Unfortunately, I don't have trean configured on my server to test.

If output has been started already, any inlineScripts (and thus any 
inlinJsVars too) are printed immediately if onload has been specified.
This happens in Trean for example, if you need a real-life example.

Not understanding this.  Even if added after page output has started, 
the text string will be wrapped in a 'dom:loaded' event, so it 
shouldn't be executed until all scripts are loaded?

Changes have been made in Git (develop):

commit 2f0d4b2305fb54c4405a202d1adcf9284c5b4a67
Author: Michael M Slusarz <slusarz@horde.org>
Date:   Fri Mar 23 13:34:08 2012 -0600

     Bug #11099: Move popup js inclusion into Horde_PageOutput

  framework/Core/lib/Horde.php              |    2 +-
  framework/Core/lib/Horde/PageOutput.php   |   13 +++++++++++++
  framework/Core/lib/Horde/Script/Files.php |   28 ++++++++++++++++++++--------
  3 files changed, 34 insertions(+), 9 deletions(-)

http://git.horde.org/horde-git/-/commit/2f0d4b2305fb54c4405a202d1adcf9284c5b4a67

If using Horde::popupJs() after the page output has already started, 
the Horde.popup_block_text is set before popup.js is loaded.