When you chose to have a stack-size bigger than 1, the price automatically gets multiplied by that number of the stack.

Say i want to sell Netherweave Cloth for 20 s each.

If i sell it in a stacksize of 1 it will go out on for 20s.

If i set a stacksize of 5, it posts a stack on the size of 5, but to a price of 5 gold instead of 1 gold.

With 20 he posts a stack of 20 Netherweave Cloth for 80 gold. (20*20*0,2g)

-Iceflare

And even sometimes with stacksize of 1, the bot posts all available. 

There is something wrong with the stacksize, i believe.  

Also problem with picking up mail on the TBC 2.4.3 client. Server is running version 2.0

I can't help with auction problem but what's wrong with mail? 

Oh, sorry. That was poorly precised by me. 
When running the Auctionbot it doesnt pick up everything from the mail. Sold/Completed auctions doesn't get picked up. It does, however pick up everything it has bought when running the bot. 

Hello, do you use wow addon? If yes try to disable all.

If this don't resolve your problem, please repport bug here: http://wrobot.eu/bugtracker/ (with log, screenshot, ...)

Yeah, i used auctioneer with this. Will try without it next time.