Sorry you are finding bugs and issues here and there. It's been a long time since some of these features were implemented in pd.
Item_backpack Doesn't Target Other Entities -- Please understand I am still no expert on QuakeC and item backpack was completed by trial and error. For the most part it works as "designed" but targeting entities is an oversight on my part. The work around would be to add a trigger_once around the backpack in question. An extra step, but easy.
it will play the default message sound, even if the 'sounds' key has a value of 0 A workaround for this is to add a noise key to your trigger and set it to misc/null.wav I'll address this in the future release since it's an easy fix.
Loading A Save Mid-cutscene Locks Mouse Aim
Please refer to Cutscene best practices on page 112 of the manual. Cut scenes are a huge hack that I borrowed from another mod. They are difficult to use in the best cases.
netname for the Quad Damage power-up
I never intended for artifacts names to be changed. See page 48 of the manual.
The BEST place to report bugs or issues is on GitHub. I am not developing pd any longer with the exception of small tweaks here and there when time permits. There will be another release some time this summer and I will address some of these you mention above.
https://github.com/progs-dump-dev/progs_dump/issues