Actually PocketBook Ukraine released the official new firmware 15.2.1 for PocketBook 301+ and recommends of owners of this model to do the upgrade.
Here are the links (pages are in Russian though, please use Google Translator f you don't reader Russian):
http://www.the-ebook.org/forum/viewtopic.php?t=15950
http://pocketbook.ua/news/press/79
Two main improvements in this version are resolution for issues with battery charging and better PDF support.
I would expect to see similar announcement from the PocketBook USA soon.
Some of my Russian-speaking buyers did the upgrade already and reported improvements comparing to the previous 15.2 version.