Issue description: Right clicking while holding a stack will increase the number of items in storage by the entire stack instead of one item.

What happens: While holding a stack of items with the cursor. Instead of dropping one item when right clicking, it drops the entire stack while decreasing the stack being held by one

What you expected to happen: Item in storage increase by one, held stack decrease by one

Steps to reproduce:

1. Click on any stack of item so it sticks to the cursor. Example: 64 stone on hand, 0 stone in storage
2. Right click into the grid inventory space. Example: Now 63 stone on hand, 64 stone in storage

...

Version (make sure you are on the latest version before reporting):

• Minecraft: 1.10.2
• Forge: 12.18.3.2281
• Refined Storage: 1.2.25

Does this issue occur on a server? [yes/no]

If a (crash)log is relevant for this issue, link it here:

[pastebin/gist/etc link here]