Ok, yeah, Tails got them, I've shift-multi-copied 3 bugs 😛. Ugh, Sorry about that!
I guess you can cofirm them with 1.5 now...
Ok, found the issue:
If your inventory is full, and you have at least a minecart, you still pick up minecarts, but it "dissapears". I accidently broke a chest while testing...
Reproduce:
"Dissapearing"
Fill double chest and inventory with Minecarts
Break 1 side of chest
Pick up Minecarts (actually works!)
"Reappearing Act":
Open inventory, throw out minecarts in inventory (not hotbar) with Q.
Close inventory, open second side of chest
Notice inventory is full again!
"Dissapearing Act:
Open inventory, throw out minecarts in inventory (not hotbar) with Q.
Close inventory, open inventory again, items are not there (they're on the floor where you threw them, duh!)
You can no longer use the "Reappering act" then...
I could not find a dupe of this bug, should I make a new one?
Crap, sorry I missed that bug report, I didn't think of searching for a feature.
I'll try to see wether I can trigger the dissapearing items or it was a figment of my imagination.
Update: While trying it in this smaller test map, items have dissapeared, since after testing, I checked the chest and it was no longer full after returning the minecarts in the chest!
Just wanted to add that I've noticed this always happens on row 0 of the x chunks: the effect can be reproduced constantly if found build a z row for every row 0 of any x chunk.
I haven't found anything significant regarding z repeptetivity yet though.
Furthermore, I've found behaviour of the activation can be diffent if coming from the side (as demonstrated in the video and images provided bu the reporter) and from the top (using block with a lever on top, activating the redstone) ie: sometimes they act the same, sometimes the switch on top works, but not the side one; sometimes the side works, but the top doesn't! The "effect" remains constant depending on your z location (respecting the x chunk rule mentioned above).
I attached a save that triggers this bug, to trigger it, simply teleport using:
/tp -742 6 -185
Note that this world has a custom NBT that spawns a custom FallingSand, that, if it doesn't exist, gets pushed by a piston (generating a wood bridge in this case).