My solution still stands as correct - Change shopper before adding items to cart regardless of the configuration that now exists.
Ah come on AH, you know better.
The reason is a hidden config, which maybe set public next release.
The default behaviour was NOT to empty cart for people that did not know of this feature as it was designed for a specific use case.
//behaviour on admin change shopper
if (VmConfig::get('ChangeShopperDeleteCart', 0)) {
Clearly the default behaviour has now been changed and is now the default - hence the reason for the report of changing behaviour of VM. Which requires - either for the person to change a hidden config - or add items to the cart After a change of shopper is made.
Latest release code:
//behaviour on admin change shopper
if (VmConfig::get('ChangeShopperDeleteCart', 1)) {