Thanks. Fortunately I saved my translation locally so it is just a matter of copy and paste to complete the translation.
Usually you can pick up discarded translations through the history, but I guess that in this case it wouldn't actually be saved anywhere other than your local copy. The browser back-button sometimes gives a local cache that can be copied, otherwise there's really no answer to this.
The main problems seem to occur when new contributors manually add translation tags (despite there being warnings all over the place against this). I couldn't see any evidence that this was the cause of this specific one, though.
KDE UserBase Wiki 