Bug with big Black Pixel on Photoshop CC

Hi,

I recently install Photoshop CC (iMac 2,8 Ghz Intel Core i5, 16Go 1333 Mhz DDR33, Mavericks)

When using different layers, I have a HUGE BLACK PIXEL coming on the picture (365x365px) , often on the low lef corner.

It disapears when I strongly zoom inside but it comes back when I zoom out...

Any idea please ????

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