Hi Zozdag,
You haven't specifically said that the default PDF viewer has changed to Reader after the update. How do you know Reader is invoked?
The property you're using should leave the default viewer unchanged. It doesn't change anything related to browser other than leaving the default viewer the default.
The delay you're experiencing could be the result of browser changes. In fact, Acrobat has deprecated its browser related preferences because 1) browsers are evolving rapidly (almost weekly) at different rates and 2) some browsers are dropping support for plugins altogether.
Also, support for IE's EPM was rolled out over time. While fully supported with 10.1.10, you should refer to Internet Explorer Enhanced Protected Mode | Acrobat, Reader for more details.
Report back if you have more information.
hth,
Ben