Problem is following:
Two USB DVB devices are used, DVB-S and DVB-T. If both devices were plugged in PC and used in SmartDVB (switching between channels), SmartDVB seems to enumerate devices (by numbers 1, 2...) instead of using their names (or whatever more precise information is available about device) to associate them with frequency lists (Frequencies->Add/Edit Frequency lists...). If on next start of SmartDVB device enumerated with 1 is not available, SmartDVB will not switch to channels associated with currently available USB device because this device is no longer enumerated with 2 but with 1.
I don't know if SmartDVB really works in above described manner, but it seems to me like that. Problem with this is that USB devices can not be disconnected and connected between usages of SmartDVB because channel switching does not work. Everything works ok if only one USB device is ALWAYS used, but problem appears if two devices are used and then USB device enumerated as 1 is removed.