Why does software update re check after updates are installed when you show updates
It appears that some updates have others as prerequisites, and will not show up as available until the others are installed. Thus, Software Update makes a list of all eligible updates, then runs. If a subsequent update was also pending that was not eligible to be downloaded because its prerequisite has not not yet been installed, that update would not make the list. The subsequent check, however, would see if any new updates had been unlocked by the updates installed.