Hello Craluminum, thanks for the quick reply.
I don't have AMA, but I have Carry On, which developed a hole new bug on its own.
If I have time today, I try to check a new Singleplayer only with your Stack Mod and report.

Thank you :)

Craluminum
The mod in question was the Anvil Metal Recovery by Melchior, with a showing of Carry On. 
I had the offending item (Metal fragments) in a Storage Vessel held on my back. 
Removed the mod, re-entered the game.
Noticed the stack changes back to baseline, attempted to re-edit them.
Reverted upon re-entering the game.
After a few tries I figured it was down to AMA, re-enabled it and the reversions to baseline ended. 
In this scenario, the entirety of the config file was affected. 

As for the digit replacement, I can say this was fully an error of my own (find & replace, "In selection" not checked, changing 1 for 8...), while trying to get all the edits over and done quickly. ^^; 

Hope this helps, Cralu. Thank you for your hard work!

DeNoven Liandris I'm not able to reproduce the bug

Hello.
I have a similar problem like DeNoven.
I close the game fully. I edit the config file, save it, start the game launcher (config file is still modified) I start my game and most of the data is reverted to original stack sizes. Like cobblestone, stone (the pebbles), sand, gravel. Others hold the stack size (128): raw clay, soil, tree logs. I play with other mods, but I haven't deleted another mod (like DeNoven).
Please tell me if I can further assist with any informations. Thank you.

Finding some issues lately; every time I close the game and reload, the config file often reverts to original stack sizes. 
Sometimes it does a full revert to default, sometimes it just replaces the first digit with the original (128 becomes 828). 

I'm not sure what's happening but the number of times it keeps happening has me pausing use right now. Sorry Cralu!

Edit: I've found the reason - because I removed a mod that added a few items, the game was reverting to normal upon seeing there was an item or two from the mod still around. It now stays the same upon re-entering the save. 

Craluminum That's fair, I didn't know if it was a general block type affected or such, since I have clue of the bug itself; at least an easy work-around is to simply carry boards and build planks as needed, if anyone encounters this. Thanks for the info! :)

Lohn I don't know whether it is the only affected block, I didn't have time to check thousands of blocks

Craluminum So is that the reason for plank block not changing it's stack size, and if so - is it the only affected block? I'm glad it was easy to at least figure out the cause. :)

Lohn I found an issue, turned out it is vanilla bug, but I won't fix it myself

@Craluminum Thanks so much for the mod! I noticed while using it, that for some odd reason planks don't seem to stack. I checked the config to ensure I didn't somehow break it, but they don't stack currently. To be clear, I mean the solid plank block made of boards. I tried adding a line without "-ud" to each but no difference, reading the lang file I can't understand why yours mod doesn't increase their stack, but I thought I'd at least tell you. :)

BlueFuryDragon ?

Wandour 2147483647 max

Awesome!!! 
is there a CAP ?