Repro Steps:

1) Add, or Select any Grid element on a page.
2) Attempt to change the background colour of the Grid by either typing:
a) #FFFFFFFF
or
b) Copy-Pasting #FFFFFFFF
into the Hex value text input field.
3) Press [Enter] to confirm.

Observe how the colour reverts to the hex value that was entered prior to inputting the newest value.
Note that the same error does not occur when editing RGB or HSB values.