AutoEllipsis=true affects the vertical positioning of the text

I see it. This looks like a limitation in the underlying winapi, DrawTextEx(). Which doesn't get a lot of help from the Label class, it doesn't turn on the DT_SINGLELINE option (aka TextFormatFlags.SingleLine) since it is capable of rendering multiple lines. DrawTextEx() documents that this is required to get vertically centered text (DT_VCENTER). So the real bug is that it shouldn't be centered at all :) Do note that you do get centered text when you grow the label vertically.

The simplest way to work around it is by setting the label's UseCompatibleTextRendering property to True.