Something was unintentionally broken by changes in 1.9.5. or 1.9.6 that now prevents merged stacks from all being mailed simply by repeatedly right-clicking on the merged stacks. Without disabling Merge stackable items, the only way to mail all of a merged stack is to toggle the equipped bag panel and essentially disable AdiBags temporarily and then find and mail each stack or partial stack. Previously, less than a month ago, it was possible to mail an entire merged stack by repeatedly right-clicking on it. I rely on this feature constantly, which is why I know the bug was introduced very recently.