Commit 5a442c0addc69d0c4b58e98e5aec1cf07576debb switched NAND (among other things) from explicitly checking autostart for "yes" to using getenv_yesno().
Instead of checking for "yes", getenv_yesno() checks for "no", and assumes "yes" if it can't find anything. This changes the default behavior, with no autostart environment variable defined, from "no" to "yes". I don't think "yes" is a desireable default for autostart[1]. README does not specify the default behavior. It also doesn't specify that autostart applies to NAND commands at all, for that matter.
Should getenv_yesno()'s behavior be changed? Are there cases where a default of "yes" is legitimately wanted (if so, a parameter could be added for the requested default)?
-Scott
[1] I'm not sure that the feature makes sense at all, as often one would need to load an RFS and/or a device tree first, not to mention that you may be trying to update U-Boot itself. Autostart doesn't do anything that you couldn't do yourself by following the load command with "bootm $fileaddr".