Android (Windows): Some plugins are compiled for the host machine (i.e. as .dlls)

I noticed that when deploying local libraries, some .dll files were copied onto my AVD (see the attached log). It turns out that there is a mix of android .so files and windows .dll files in (for example) C:\Qt\Qt5.1.0\5.1.0-beta1\android_armv7\plugins\imageformats

I guess this means that either:

1: The Windows releases of the Qt libraries for Android are being built on Windows and there's build/host/target confusion in the pro files for these plugins.
.. or
2: A build directory was re-used for both the Windows and Android builds, so the dll files were not cleaned first.

If 1: In the Necessitas days, the actual Qt libraries/plugins were always built on Linux and we only compiled the tools on Windows itself (actually, for the last 2 releases we switched to cross compiling the Windows tools on Linux with MinGW-w64 cross compilers). Maybe going the same way would safer for the 5.1.0 release? In some ways, I like the idea of compiling Qt for Android for Windows on Windows; it provides a lot of testing of the Android tools (all of them, Qt tools, Android NDK, Android SDK, mingw32-make), and ensures that we don't make incorrect assumptions.

If it's not 2: then please let me under know which environment (cmd.exe or MSYS) the Qt libraries for Windows are being compiled so I can dig into this some more.

The full list of dll files is:

plugins/iconengines/qsvgicon.dll
plugins/iconengines/qsvgicond.dll
plugins/imageformats/qmng.dll
plugins/imageformats/qmngd.dll
plugins/imageformats/qsvg.dll
plugins/imageformats/qsvgd.dll
plugins/imageformats/qtga.dll
plugins/imageformats/qtgad.dll
plugins/imageformats/qtiff.dll
plugins/imageformats/qtiffd.dll
plugins/imageformats/qwbmp.dll
plugins/imageformats/qwbmpd.dll
plugins/sensorgestures/qtsensorgestures_plugin.dll
plugins/sensorgestures/qtsensorgestures_plugind.dll
plugins/sensorgestures/qtsensorgestures_shakeplugin.dll
plugins/sensorgestures/qtsensorgestures_shakeplugind.dll
plugins/sensors/qtsensors_dummy.dll
plugins/sensors/qtsensors_dummyd.dll
plugins/sensors/qtsensors_generic.dll
plugins/sensors/qtsensors_genericd.dll
qml/QtQuick/Controls/plugin.dll
qml/QtQuick/Controls/plugind.dll
qml/QtQuick/Controls/Private/privateplugin.dll
qml/QtQuick/Controls/Private/privateplugind.dll
qml/QtQuick/Layouts/qquicklayoutsplugin.dll
qml/QtQuick/Layouts/qquicklayoutsplugind.dll
qml/QtSensors/declarative_sensors.dll
qml/QtSensors/declarative_sensorsd.dll