Burner operating with no input

Issue description

Burner connected to a belt of sulfur is burning sulfur forever. Internal buffer will not go down.

Reproduction steps

Internal buffer seems to be stuck when import trucks are turned off. Turning trucks back to auto or on makes the buffer go down.
Didn't see what caused the issue first.

Game version and build number

v0.6.0d b322

Operating system

Windows

Attachments

Bug unlimited sulfur burning.save

Files not imported: Bug unlimited sulfur burning.save

The burner had a back up sulfur in its buffer upon load (8 in this image)

After I let it run for a bit it eventually burned through the buffer and stopped working:

I cannot reproduce this issue as I believe it is working as intended.