I would not get too excited. On further questioning it sounds like this should not apply because I use the InstallOnOpen:true flag. But the nature of the disappearance sounds very much in keeping with what was described so it’s worth testing.
The fact that the app says (not installed) before and is installed after pressing “done” seems pretty exciting to me.
We are definitely looking at a bug. Either InstallOnOpen doesn't work as advertised or it is not implemented as documented, because opening the app (even explicitly) doesn't remove the (not installed) title padding. Only pressing “Done” seems to, as per title shown in the PDFs.