I'm using Packing Tape with Factorio 2.1 Final and the Warehouse mod. I've set the Warehouse's capacity to 2000. When I then pack it into my inventory with Packing Tape active, it only picks up the Warehouse with a capacity of 1800 and drops 200 on the ground. This problem affects versions 21.0.3 and 21.0.4. If I use version 20.0.9 and modify the Info.jsn file for Factorio 2.1, I don't have this problem.

What are you using to edit the size of warehouses? I don't see an option in the mod to do it, so are you using a custom mod? I suspect you're editing it after I create the packed chests, and the reason the old version works is because I had to make them much larger than necessary to work with quality in 2.0.

I use this mod for the stack size change of the Warehouse mod.

https://mods.factorio.com/mod/warehouse-resize_2

This mod gives me the option to change the stack size in the mod settings.