Just for confirmation, you are recording in TS format, aren't you?
I ask because I'm not sure how this would work when recording in JTV format, because the Time Shift files are the recording, essentially.
But I suspect that the new folder would only be used for TS recordings that start while a channel is in Time Shift mode, since once a Time Shift session has started the location of the Time Shift files couldn't be moved.
Ah, actually, I just re-read the item. I think it is working correctly, because the new functionality says "alternative hard disk for TV recording and time-shifting", so the new location holds both types of files. MC is just load sharing between the two. It doesn't sound like the intention was to put recordings in one location and the Time Shifting files in another location, but to put both file types into both locations. Which answers my queries above.
Perhaps Yaobing can explain the rules, but I imagine it is something like, if one recording is already being saved to drive A, then the second recording is placed in drive B. Or it could be based on free space. But more likely which drive is in use, and which is not being used for TV recordings at the start of a new recording.