Just to add a bit; We have been extremely inundated with support topics in the past two weeks so we are significantly slower in responding.
In the future, self posting actually pushes the topic back in our Queue system which adds an additional delay. Its not the best system it seems but its how it works for now.
As for the issue, if you've already tried regenerating your thumbnails I would suggest first disabling any plugins you have running. Just in case there is a conflict. This issues usually works itself out with a bit of refreshing of things so thats the next step.
Remove the images from the posts, update them, then re-add them in. Check the visual bug again and see if its resolved. If not, go to the portfolio settings for that portfolio. I assume its in your dynamic template for that page so thats is where you'll need to change the settings. Deactivate the grayscale hover effect and save the template. Now, re-activate it and save again.
Let us know how it goes and if it continues we can look deeper to see if there is something specifically causing this on your installation that is outside of the norm.