And (re-)found a generic bug that has been around for some time now:
When you have a bundle on your back (like grass, branches, twigs, etc.) and you cancel a sell order, the stacks are merged (so far so good) - but for some reason (BUG !!!) when you have like 3 bundles (4 is max) and you cancel a sell with 3 stacks, you get only 4 on your back - 2 are lost (forever).