The buttons on rowediting plugin in a grid are covered by the errors tooltip when validation fails on any column. This is specific to a grid in a window. I have tested that this breaks in 6.2 and is still present in 6.5. In 6.0, the error is displayed to the right of the grid, outside of the window.

https://fiddle.sencha.com/#view/editor&fiddle/203o

rowEditing_6.0.0.640.pngrowEditing_6.2.0.589.png