为什么“adb install -r”会卸载旧版本的应用程序？

I'm testing a complete rebuild of my application and want to make sure that the update will go smoothly. I'm having an issue when I have the old version and perform the "adb install -r" command. What I expect to happen is it just replaces the old version with the updated version. What happens is that the command line reports success but all it did was uninstall the old version and did not install the new version. I have tested this on a Galaxy Nexus with 4.2 and I have this problem but when I tested this on an S2 with 4.0 it works as expected and replaces the old version. Any ideas why this would happen on the GS and not the S2? Also will this happen to my users when they try to update the app from the market?I'm testing a complete rebuild of my applicatio