When I have a lot of items in the queue (for example 5000 rails - don't ask), or almost no space left in my inventory, and I switch to front queueing, once I craft something else, some of my crafts will be cancelled and a lot of items will spill to the ground.
I assume for the front queueing you cancel all jobs, implement the new one and then re-start them? That might explain this problem.

This problem should have been fixed in one of the recent updates. Are you sure you have the most recent version? What version of factorio are you running?

I'm always using the most recent experimental release. I can confirm that the issue was still there yesterday.

Hmmmm. I'm not able to reproduce the error. What items are in your queue when this problem occurs? Do you have any other mods that affect your inventory or the hand crafting queue?

The mod works in the way that you suspect except it temporarily expands your inventory to account for spillage. It's not a pretty workaround but I haven't had a problem with it. I may just be able to fix it by just increasing the amount by which the inventory expands but it could also be some weird interaction with another mod.

ok yea, I was able to reproduce the error. The problem comes when you build a big queue, refill your inventory, and then build the queue even bigger. I will fix.