Sprite Editor and Grid size problem

Hello, I'm looking for some help with Sprite Editor and it's Slice function.
I have a little bit specific size Sprite Sheets - 4096px x 256px. As you know size is PoT. What do i do next:

- set Sprite Mode to Multiple
- go to Sprite Editor
- click Slice
- change Type to Grid
- put Pixel Size Y to for example 200

Now when I change input to any other in Slice box it will automagically change above value from 200 to 128.
Can you guys please tell me if it is some kind of desired effect or just a bug?
I cant change size of Slice-Grid function only with horizontally big images (huge width and small height). I haven't try it with vertical images tho.
Btw. I can change size of each wrong sliced frame "by hand" but it's a lot of work when you have many of them.
Thanks everybody!

 

Hello again. I found an answer myself.
What I had to do was:

- select Texture in project folder in Unity
- click Override for Standalone in Inspector
- set max size to 4096

After this change slice function works well.

 

This helps me! Thank you.

Before I find it, I've lose about two hours with wrong grid.