Finally we got it. These strange texture loading problems are hunted down. The reason of these issues were the sucking support of NPOT-textures by the ATI drivers. Resizing all textures made the crippled texture problem disappearing. Even the multiple texture loadings which were caused due to a bug in the texture handling of Irrlicht could be fixed.
While this major problem of the last few days got fixed another major problem with the physics system occurred. One of the newest features, the “UserDefinedPhysicMesh”, which allows the user to import an arbitrary mesh into his custom map, doesn’t work as intended. Further information on this specific topic in the next days.
Problems appear to be fixed!