My guess is that the file was exported as ASCII with some non-English code page that collides with UTF-8.

This is normally an issue with the material not having the correct path to the texture. It's not related to the exporter.

Looks like that version of Source doesn't allow vertex animations to move a vertex by more than 8 units.

Vertex animation was added for Dota 2, so it's not very surprising that older games don't support it properly.

It's the new PointerProperty which changes behaviour. It adds a user to each object in the scene export list and thus causes Blender to not delete them from the Blend file when they are removed from the scene/view layer. (I was evidently wrong when I said that deleted objects remain in the Blend file until it is closed.)

Immediately after the object is removed the scene's export list is updated, the PointerProperty is removed, and the user count is decremented. But by this point Blender has already decided not to delete the object fully.

The extra user is annoying, but I'm not in a rush to change this. Even if I did change it, you still cannot assume that deleting an object from the scene will remove it from the Blend file: the object could have additional users for many reasons, e.g. from modifiers, other scenes, or a fake user. You should keep the changes you made to your script.

I don't know which DMX formats Garry's Mod wants, so I can't include it in the add-on. If anyone does know, I'll add it as a recognised engine branch.

Are you using two different versions of Blender?

Looks like one of the script files is outdated. If restarting Blender doesn't fix this, delete C:\Users\thebl\AppData\Roaming\Blender Foundation\Blender\3.2\scripts\addons\io_scene_valvesource\ and reinstall.

Normal means that it's intended behaviour in the core Blender application. This has nothing to do with the Blender Source Tools, which doesn't handle deletion of objects or set fake users (except on import, for Actions).

This is normal. Deleting an object from the scene doesn't immediately remove it from Blender.

However, objects without users are not saved to the .blend file. You should find that the armature is gone after you reopen the file.

If this is not the case, then it still has a user, or has a fake user.

It sounds like your curve object isn't parented to anything. Try making it a child of the object that you are trying to align it with.