Unagi with Gaia 184.108.40.206-prerelease 20130418070205 Searching in Everything.me, long tapping a result, adding it to the homescreen and long tapping it again still offers to install it. Seems like the check if the app is already installed is only performed when retrieving search results.
Is it the same bug than bug 866502?
I believe so. aryx, can you check the patch from bug 866502 and see if it resolves this issue for you?
Bug 866502 has the same steps to reproduce > Duplicate.