This is a bit of an odd one, but I think in terms of data continuity and exactness it is needed.

When adding a determination, a valid taxon has to be entered. This is wrong, as the determiner may have recorded a taxon that doesn't exist (for whatever reason: spelling, wrong genus/species combination etc. etc.).

Obviously you could add the taxon to a checklist, but I'm not sure if that would "right", and going through all the add taxon boxes when all you have is a name is a bit long winded.

Maybe if on entering an invalid name, instead of bringing up the search box the user is prompted "this name is invalid, do you want to search or add it to the list of invalid names?" - not a checklist as such, but just somewhere to dump the invalid names?