To make sure, that this function is added by a plugin try to open the file with
vim --noplugin <filename>
If the cursor doesn't jump to the position of the last edit you should open the file again without the --noplugin
-switch and study the output of :scriptnames
. :scriptnames
lists all previously sourced scripts.
If you are a semi-experienced vim user you can exclude most of the scripts by means of the path. For instance, all scripts located under &rtp/{ftplugin,spell,colors,syntax}
(&rtp := runtimepath) are out of question.
I can imagine, that the script which implements this feature has a related name.