Instead of debugging your Roundcube, look for history!
Say you have an install of Roundcube.
Say you log in as a user, log out, and re-login (that or any other user).
Say you expect it to work.
It will, but not on the first try.
line This gem from 2005 sums it up. http://roundcubeinbox.wordpress.com/2009/08/
* After I log out, the first login after that always fails. Second one succeeds.
And Split Enz says, "History Never Repeats". I have to disagree.