Multiple Tomcat Instances behind HTTPD - Session Expired

Apache HTTPD 2.2
Tomcat 8
Vaadin 7.6

Currently setup with multiple Tomcat instances, each on their own port, being proxied to via HTTPD (depending on the URL):
Tomcat 1 hosts APP_1 on ajp port 8009
Tomcat 2 hosts APP_2 on ajp port 8010 is proxied to ajp://localhost:8009 is proxied to ajp://localhost:8010

Each work just fine independently, however, the following error is encountered:
1. APP_1 is opened in one tab of the web browser; navigated through for a few clicks
2. APP_2 is opened in another tab; navigated through for a few clicks
3. Reverting back to APP_1 yeilds a “Session Expired”

It looks to be an issue with cookies. The JSESSIONID is being changed after using APP_2, and it attempts to connect back to APP_1 using the new JSESSIONID. It seems to be a well-documented issue, but I have been unable to find any resolution. Any ideas?

Thanks in advance!