Reproduction
Throw two of the same unstackable item on the ground and pick it up. You will get a stack of 2.
Throw a stack of 64 and a single item of a stackable item on the ground and pick it up. You will get a stack of 65.
If you attempt to pickup a stack higher than 127, it will disappear. Minecraft can only handle stacks below 128.
Video guide: https://www.youtube.com/watch?v=OHPk7LSOlrc
Reproduction
Throw two of the same unstackable item on the ground and pick it up. You will get a stack of 2.
Throw a stack of 64 and a single item of a stackable item on the ground and pick it up. You will get a stack of 65.
If you attempt to pickup a stack higher than 127, it will disappear. Minecraft can only handle stacks below 128.
Video guide: https://www.youtube.com/watch?v=OHPk7LSOlrc