Checkbox disappear when mouse hovers over it after the upgrade

Hi,

We upgraded BPM to NW 7.4 sp6 and after the upgrade we are seeing an issue with checkbox.

Whenever the mouse hovers over the checkbox, the checkbox disappears . It is still possible to check the checkbox ...

Any idea if this is a bug or some configuration on the portal has to completed after the upgrade.

Best Regards,

Pavan