I had this happen several times. Either the app completely disappeared or in some cases the icon was still on desktop but when I try to open it says it its not installed. I never moved any apps to sd card either.
But I did read somewhere what was causing it. For some reason, some apps were automatically installing in the media area. This is what was causing the issue.
Go into manage apps, applications, then click on the media tab along the top. Scroll through the list and if any app has a checkmark, remove that checkmark.
I have not had a repeat since doing this. Of course, any new apps you dl, it is good to check and make sure it did not go into media area.
Sent from my DROID BIONIC using DroidForums