If a simple image move from one hard drive to another causes a total crash, Capture One, might want to look at a work around for that. In other software with catalogs, you will just get a ! point telling you the image is no longer found in the catalog and you can quickly browse, find it and then update the catalog.
I don't use C1 in catalog mode, only session, as I still prefer a session methodology. I have seen this same type of error in session mode, where it seems C1 has somehow lost the data from the last session, however it just lets you open a new session and continue.
Also to be forced to move images from one drive to another via Capture One to maintain catalog consistency seems a bit excessive to me.
Just glad that Capture One still has both options, session and Catalog.
Correct it shouldn't happen at all and yes, 'normal' operation is that a ! is shown on the missing image.
Unfortunately these things do happen on extremely rare occasions and we have a number of tools to repair a catalog if need be, as described earlier (repair / verify Catalog). Not to mention a support department with an average response time of around an hour and no more than 24 hours.
I don't think its fair to say that C1 Catalog's are unstable (I know not your words Paul), and that users should avoid them.
We have many happy customers using Catalogs.
Most importantly if you do have an issue, don't suffer in silence and let support help you.