Library changes not always detected

I was opening an old project on latest Ubuntu 16.04 PPA Nightly and had a couple of warnings about changes on symbols.
I fixed these and then browsed the schematic and spotted two parts had been drawn as disconnected square boxes, an inductor and a zener diode.
This was because the symbol names in device.lib have changed, but the lack of warnings is the problem here

Raised as a bug

Sometimes I have to rebuild the symbol cache so this is dangerous

With old projects I work this way:
-Rename the cache lib as myproject.lib
-Add myproject.lib to the project
-Remove any other lib from the project

If I need to add a new component that is not in myproject.lib, I add its lib, copy the symbol to myproject.lib and remove that lib again.

I have found that I have to flush stale parts out of the cache sometimes or I get nagged about “rescuing” the old symbol, even though I have switched to the new one, when a symbol shape gets modified.

I can manually edit it out, but deleting and rebuilding should work.
Silently failing to load is just wrong.
The bug report shows the square box with two question marks