Doesn't work with filter 'pre_set_site_transient_update_themes'

[itailulu]

For some reason this script doesn't seem to work with my custom Genesis child theme, when using the filter 'pre_set_site_transient_update_themes'.
It does work after i changed it to 'site_transient_update_themes'.

I also tried to change priorities, but it still didn't work.
Any idea why?
Are there any disadvantages when using the 'site_transient_update_themes' filter hook?