I think the problem is related to the usage of wrap_content on so many levels of your layout. I have seen that this causes the individual items trying to be smart sometimes and are auto adjusting incorrectly or at leas in an unexpected way. Try to put your buttons on top level layout to test if you can get the correct behaviour when using match_parent instead.
But in the end, playing around with combinations of wrap_content and match_parent can consume quite lot of time. A fast way forward may be to set the buttons to fixed size, but then please make sure you set them somewhat bigger than you think is enough to make sure it will work on many different screen sizes.