I use a t:colorfield in a modal popup, after selecting a color from the color popup the base popup disappears. It gets visible again when I click somewhere in the workplace.
Could you - when finding some time - record a client log?
Start the client with client parameters
(.) loglevel=ALL
(.) clientlogfile=c:\temp\cc.log (or whereever you want to store the log)
Then navigate to the screen in which the problem occurs and then close the client.
Now send the file (the file is cleaned the next time you start the client.)