"HTTP session already opened" when calling HoptoadNotifier.notify()

[findchris]

Hello all.

Has anyone seen the message "HTTP session already opened" from hoptoad
before?

The stack trace looks like:
>>
/vendor/plugins/hoptoad_notifier/lib/hoptoad_notifier.rb:136:in `new'
/vendor/plugins/hoptoad_notifier/lib/hoptoad_notifier.rb:136:in
`build_notice_for'
/vendor/plugins/hoptoad_notifier/lib/hoptoad_notifier.rb:94:in
`notify'
/app/models/my_model.rb:88:in `do_stuff!'
>>

FWIW, line 88 of my_model looks like this and lives within a rescue
block:
>>
HoptoadNotifier.notify(:error_class => "Something
Strange", :error_message => "!!! Exception caught: #{$!}")
>>

I'm using Hoptoad Notifier v2.0.18.

Cheers,
Chris