OpenMW fails to load certain particle effects in .osgt format

Openscengraph has a repository of example files. I tested the following two to see how particles can be created for the Example Suite. Both of them open properly in osgviewer (apart from the missing textures, but that's not important here).

• https://github.com/openscenegraph/OpenSceneGraph-Data/blob/master/fountain.osgt
• https://github.com/openscenegraph/OpenSceneGraph-Data/blob/master/SmokeBox.osgt

When using the files in OpenMW and OpenMW-CS

• fountain.osgt renders properly
• SmokeBox.osgt is not rendered and produces the following report

[13:21:00.737 W] InputStream::readObject(): Unsupported wrapper class osgParticle::ParticleSystem
[13:21:00.738 W] InputStream::readObject(): Unsupported wrapper class osgParticle::ModularEmitter
[13:21:00.738 W] InputStream::readObject(): Unsupported wrapper class osgParticle::ModularProgram
[13:21:00.738 W] InputStream::readObject(): Unsupported wrapper class osgParticle::ParticleSystemUpdater

The most obvious difference between the files is that one contains mesh geometry while the other has only the particle system.

I'm using OpenMW 0.48 RC2 from https://forum.openmw.org/viewtopic.php?p=73161#p73161