Killdry problem / query.

Can anyone explain the killdry function in more detail than the manual?  It says it should be engaged when used in a parallel effects loop.  I'm using it in mono (left in/out) on the effects loop of a Line 6 Flextone combo amp and I'm not sure if this is a parallel or serial loop?  When I first powered up the setup I had Killdry on and the unit seemed to function fine.  The  G Sharp settings came in when I activated the FX loop on the amp by pressing the appropriate button on the Line 6 FBV shortboard foot control.  I then tried it with Killdry out and also tried the serial / parallel mode setting on the G Sharp just to see what the differences where.  After I did that it started acting strangeley, some times with a dodgy sound when the G Sharp was engaged with the Line 6 floorboard through the effects loop, and when the loop was turned off with the killdry on it lost the signal completely to the amp?  This was dfferent from when I first tried it with the killdry on.  Now it will only work as expected with the killdry off in the serial mode.  I rebooted the whole thing but it's still the same (i.e. not acting as it was when I first powered it up, when the killdry didn't seem to cause problems).  Any idea anyone (hope you can understand my gobbledegook!).  Thanks.