This is a bit complex to explain, so bear with me.
What I'm doing: C++ app that uses QDeclarative* classes to:

• load an initial [ROOT ITEM].qml (main view of my app, always present)
• inject/remove from the scene other [ITEMs].qml (views stacked on the top of my main view, and controlled through signals emission)
• a "bridge" object exposes some C++ calls to the QML space, to allow QML components to do things outside the C++ space.
• I call QDeclarativeEngine::setBaseUrl() to set the base url.

Every QML Item is a composition of other smaller items. Those are held in a directory structure like:

• MainView.qml
• SecondaryView.qml
• MainViewComponents/subcomponent1.qml
• MainViewComponents/subcomponent2.qml
• MainViewComponents/subsubcomponent1.qml
• SecondaryViewComponents/subcomponent1.qml
  and so on...

The Views import their "components" using: "import 'MainViewComponents'"
Subcomponents do the same with other "sub-subcomponents".

The QMLs are ALSO imported in a QRC file: in this way there is no need to bring around the files.
QDeclarativeEngine::setBaseUrl() infact works also with a "qrc:/qmls/". In this way I get the maximum flexibility.

Problem: when running this kind of stuff on Maemo5, I get messages like "Type [my type] unavailable".
I tried WITH and WITHOUT the usage of QRC-based URLs. No difference.

Sorry I can't provide the actual code: I tried to explain as much as possible.
NOTE: I'm still trying to figure out the cause. I'll try to find an actual solution.

UPDATE (2010-03-22):
Seems like the problem was a "chain" of "component unavailable", caused by the fact that the first element to be "unavailalbe" is the WebView.
Adding a very basic test .QML that shows the problem: webviewtest.qml.
Try to run it with a:

1. /opt/qt4-maemo5/bin/qml webviewtest.qml

result will be:

file:///home/user/webviewtest.qml:4:1: Type WebView unavailable
WebView {
^
Wall startup time: 28

This doesn't happen on other platforms.