Arduino IDE - strange effect (SOLVED)

Hi, maybe someone here has an idea, what is causing this

Changed two days ago from DEBIAN stretch to Linux Mint 18.2 Xfce.

Did not encounter that under Arch Linux, PCLinuxOS and Debian (all Xfce) ..

Any guess, please?

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The image is so small it's hard to see. Is the name of the currently selected board not shown in the menu?

Just click on the image and it opens to full size.

The text, when selected, of board, port and programmer is missing, when selected.

Strange ....

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Seems, this happened before ...

Again Linux Mint.

It is a Xfce theme feature ...

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