Tested it on 0.18.6 with seablock
When pasting a configuration from an existing inserter, the pickup origin link doesn't get updated to the new configuration's pickup position, allowing for some wacky early game inserter "optimization" bordering on cheating

Reproduction steps:
Put down an inserter as normal, making sure it would be correctly picking up items as it should
Put down a second inserter, doesn't have to be powered
Set its pickup and drop down points to be the same tile, making sure to orient them so that the drop down coincides with the first inserter's current drop down without having to rotate
Copy the new inserter configuration, paste it into the original inserter
First inserter should pick up and drop down item in the new configuration as if it was still picking it up from the same origin point of the old configuration

I assume this to work the other way around, too, as a normally non-functional configuration will not update correctly and cause the inserter to simply never pick up anything in the newer one, if its original configuration's pickup point didn't have anything to pick up

It doesn't seem to occur anymore on 0.18.7

The issue seems to be back again in 0.18.9, or may have not gone away at all.
New information on the setup, both the output and the input tiles should be empty at the time of the pasting, as in the inserter shouldn't be able to pick up any item from either the original output or the original input once you go pasting the same-tile-configuration, otherwise it will just switch to the new configuration as it normally would.