1) For the purpose of this test, I lowered the persistence of the Blue Mountain Bag, from 8 hours to 2 minutes //I did so using a custom types override file defined in cfgeconomycore.xml (see video).//
2) I also lowered the server's item despawn distance from 100m to 10 m (CleanupAvoidance in globals.xml). //I did this to make it easier to see what was happening rather than going far away.//
3) Place one of the persistence altered blue mountain bags on the ground.
4) Put a single bullet in the blue mountain bag and wait 60 seconds.
5) Now add an additional bullet onto the **existing stack** inside the mountain bag to make a stack of 2 (or any size for that matter <= max).
6) Move at least 10-15 meters away //(Note: this distance is based on step (2) of changing CleanupAvoidance in globals.xml. It is 100m by default and a closer distance will allow the bag to despawn at this shorter distance.)//
7) Adding the bullet in step (5) should keep the bag alive for another 120 seconds per the adjusted persistence time as its contents were effectively changed.
8) However, the bag despawns within 60 seconds proving that adding the bullet had no impact **(bug/problem - adjusting the stack size - or merged/combined quantity - should reset the timer)**
NOTE: As note above, as far as stackable items go, I only tested with bullets, but I suspect other stackable types (rags, vitamins, etc) will behave the same way.
**I also tested with alcoholic tincture** and found the same issue, so I suspect all percentage based combinables/mergeables/stackables (iodine, etc) behave the same way.
** When I did this test, I used 3 bags to differentiate between bags. See my video linked above.
*** I found setting persistence times below 120 seconds problematic as the CLE seemed to do it's own thing and not always persist the full time. Especially for times below 20-30 seconds. For that reason, I stuck to 120 seconds as it also made my test easier to perform.