If you've seen my posts in the past, you'll know I never give out timeframes or ETAs. So many things happen behind the scenes for updates to happen that there's not a realistic way to offer a guesstimate of when something will be released.
I did speak with our email team about this problem today so they know it's on the radar and that it's fixed in 1.5.3, so they are actively working on getting that updated. Since Roundcube has a unique RPM (an in, it's not tied to a particular cPanel version) it is a bit more independent than some other areas. If I hear more from my end I'll be sure to post.