I just moved a medium metal handle onto a metal bolt in my inventory. Game crashed. When I returned the handle was where the bolt was, but the bolt was gone.
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Just logged in after another crash. Dropped a small metal sheet and metal rivits (studs?) moved some metal screws to another location, sorted some scrap, and it left an empty hole in inventory. When I moved three bolts into the hole, the hole flashed red and bolts were gone. At this time when I mouse over the place where the bolts were and the place where I wanted them to go, both slots flash red/pink. Other empty slots do not do this.
The inventory slots are now permanently unuseable. Screenie here: