Attaching "LTS Mk1 Side Tank (tiny)" to "LTS Mk1 Core Tank (tiny)" creates issues

[Gordon-Dry]

After attaching the first pair (radially only 2 are possible), I tried to attach another pair one the remaining two nodes.
This was impossible, the tanks "flickered".
This was written to the log on each try:

[Part ChopShop.LTS05side] [ModuleB9PartSwitch 'fuelSwitch'] Switched subtype to LF/O
 
(Filename: C:/buildslave/unity/build/artifacts/generated/common/runtime/DebugBindings.gen.cpp Line: 51)

ArgumentOutOfRangeException: Argument is out of range.
Parameter name: index
  at System.Collections.Generic.List`1[PartResource].get_Item (Int32 index) [0x00000] in <filename unknown>:0 
  at DictionaryValueList`2[System.Int32,PartResource].At (Int32 index) [0x00000] in <filename unknown>:0 
  at PartResourceList.get_Item (Int32 index) [0x00000] in <filename unknown>:0 
  at Part.OnCopy (.Part original, Boolean asSymCounterpart) [0x00000] in <filename unknown>:0 
  at EditorLogic.createSymmetry (Int32 mode, .Attachment attach) [0x00000] in <filename unknown>:0 
  at EditorLogic.<SetupFSM>m__D () [0x00000] in <filename unknown>:0 
  at (wrapper delegate-invoke) Callback:invoke_void__this__ ()
  at (wrapper delegate-invoke) Callback:invoke_void__this__ ()
  at (wrapper delegate-invoke) Callback:invoke_void__this__ ()
  at KerbalFSM.UpdateFSM () [0x00000] in <filename unknown>:0 
  at EditorLogic.Update () [0x00000] in <filename unknown>:0 
 
(Filename:  Line: -1)

ChopShop.LTS05side
 
(Filename: C:/buildslave/unity/build/artifacts/generated/common/runtime/DebugBindings.gen.cpp Line: 51)

After removing all LTS parts , the decoupler icons still resisted in the staging list.
I had to save the vessel and reopen it to get rid off these.

Full log and stuff:
https://www.dropbox.com/s/9wyfvbq5aat73h2/2018-10-26_1%20KSP.log%20and%20stuff.7z?dl=1

[doktorjet]

Weird thing... Never seen it.
LTS side tanks are designed to be attached strictly in pairs with 2x symmetry.
When you attach the first pair - it gives you 2 symmetrical virtual nodes to attach second pair. It's fully stock node-based mechanic with zero coding behind.