Bug with DataGridNumericUpDownColumn

[ghost]

Reproducing: I have a datagrid with severall columns. One of them is a NumericUpDown. I have 4 rows of data (see pics). I go click on up or down increment on first column, then go focus (click) on 4'th column, first column text should dissapear ( goes white), click up/down on second column, go again on 4'rd and observe, up/down on 3'rd, go 4'th. By the time you increment/decrement all first 3 rows, when you click on 4'th it looks something like in pic 1. Go to first row and click on it. Values change color and are visible again (pic2). Go and hover over any of the invisible columns while 4'th selected. You can see that the text is there but turns white (pic3).
EDIT: also happens if you use up/down keyboard keys instead of buttons :(....
EDIT2: also happens when I type the numbers manualy....

(as of posting date)
Latest version of MahApps.Metro, BaseLight theme Blue accent.
Latest Windows 7 64 bit
Visual Studio 2013

// EDIT: could someone please also tell me a quickfix to this please? I'm new to WPF and don't know that many things about themeing yet.

pic1

pic2

pic3