Activity Stream shows minor edit even when not asked to under some circumstances

To reproduce:

• Create a new page with the following content:

{{groovy}}
if (request.getParameter("confirm") == "1") {
  def mydoc = xwiki.getDocument("Sandbox.TestPage1")
  mydoc.addAttachment("test1.png", "content1".getBytes())
  mydoc.save("test1", true)
}
{{/groovy}}

• Add ?confirm=1 to this page URL to execute its code
• Check the history of Sandbox.TestPage1 and verify that the attachment addition was done as a *minor* edit
• Go to the activity stream and you'll notice that the change is displayed even though it's a minor edit and thus shouldn't be shown by defaut