QIcon::fromTheme() behaves inconsistently across different Linux desktop environments

In GNOME:

• Set desired system icon using GNOME Appearance tool.
• Start Qt application that sets action icon's using QIcon::fromTheme(), e.g:
  ui->action_Open->setIcon(QIcon::fromTheme("document-open"));

Expected and observed result:

• Action icons are rendered with icons from theme specified using GNOME Appearance tool.

In Xfce:

• Set desired system icon using Xfce Appearance tool
• Start Qt application that sets action icon's using QIcon::fromTheme(), e.g: as above.

Expected result:

• Action icons are rendered with icons from theme specified using Xfce Appearance tool.

Observed result:

• Action icons are rendered with icons specified for GNOME.
• Calling QIcon::themeName() returns the name of the icon theme set in GNOME

In Openbox, IceWM, Fluxbox:

• Set desired system icon theme in ~/.gtkrc-2.0
• Start Qt application that sets action icon's using QIcon::fromTheme(), e.g: as above

Expected result:

• Action icons are rendered with icons from theme specified in ~/.gtkrc-2.0

Observed result:

• Action icons are rendered without icons
• Calling QIcon::themeName () returns "hicolor" as the theme, independent of what's specified in ~/.gtkrc-2.0 and what was set for GNOME

Note that the same behavior is observed in Qt Creator itself (v2.1.0, user install from Nokia download) – namely that it has incorrect or no action icons in DEs that are not GNOME.