Hi,
It turns out this is more cosmetic than functional. When the error appears I can ALT-TAB back into the interface and it resumes OK.
The error appears when:
1. Clicking on an item (lifts the item up)
2. Clicking again (dropping the item into another position)
3. Clicking on the icon to close the inventory window
So, every time I try to change weapon the error occurs three times. However, the game doesn't bomb out, and it only happens on industrial maps.