I posted about this problem on a more appropriate forum (Technet and Technet) but I haven't received useful help so far.

Basically, I enabled folder redirection for the Desktop and the My Documents folders in our small office (SBS 2011 with clients running Windows Vista/7 64bit). When users are away from the network or simply offline, Taskbar icons do not show up when they first log in (they need to log in a second time in order for the icons to appear on the taskbar). If I disable redirection of the Desktop folder only, the icons appear correctly on the taskbar, but when users are away from the domain or offline, the My Documents folder does not appear even when Offline files are enabled...