The size of the Dpad, when smaller, should expand the inventory bar, no matter what. But if you have split controls on, no matter what size the dpad is stays at 5, but if I turn off split controls, it goes to 7 even if I expand it.
To repeat it:
Go into the latest version.
Open up any world.
Shrink the dpad until the most inventory space is shown.
Turn on split controls.
Exit and CLOSE DOWN MINECRAFT.
Reopen mine craft.
Open any world.
The inventory space is small. Move the dpad size bar.
Shrink the dpad size
Turn off split controls.
Move the dpad size and watch the inventory bar.

Their you go

The picture shows what I am talking about. It is a little blury, but you didn't make it able to take screenshots.

The glitch was found on a 7" tablet, the picture is taken on that 7" tablet, the game was on a 4.3" tablet for the picture. Use a 7" tablet for the test.