Describe the bug
When having a vertical split using the fat layout with 3 or more windows, the window doesn't stretch all the way down.

in this screenshot, you can see that with only 2 windows, it's working as expected:

but when I add a third window, this happens:

The window doesn't stretch all the way down for some reason.

Also I notice that this only happen if I have multiple tab (tab bar is visible)

To Reproduce
Steps to reproduce the behavior:

1. create fat layout (haven't try on other layouts, but so far only notice it on fat layout)
2. have the tab bar visible
3. open 3 or more window

Expected behavior
windows stretch all the way to bottom and no graphical glitch visible

Environment details
OS: Mac OS Mojave

Additional context
Try to reproduce the problem with kitty --config NONE

After trying with no config as suggested, I think the problem is that kitty still thinks that there is a tab bar at the bottom even though I've set my tab bar at the top.