Command-line batch export is broken

Not sure if it happened with the latest upgrade, or the one just before, but command line PNG export is apparently broken. I've been using a batch file for months as part of a UI spec workflow, so the system context has remained stable. When the export command fires, Mockups loads and reads the first file in the sequence, but then hangs as a background process -- I have to use the task manager to kill it.

The "Export All Snapshots" menu option is working fine, and has provided a temporary workaround. But I've got some projects that have forty or more screens edited between versions, and batch processing is a much better way to go.

Can command-line export be repaired?