Here’s one of those little things that seems to be tripping up a number of Lightroom 1 users who have upgraded to Lightroom 2.
In Lightroom 1, you can expand the Keywording panel and start typing a keyword into the big keyword tag field. As soon as you start typing, Lightroom offers an auto-complete option by displaying any of your other keywords that match the letters you’ve typed so far. This is a handy feature and people have come to rely on it.
However, in Lightroom 2 there is a new field just below that larger field in the Keywording panel. Depite its subtle label that reads “Click here to add keywords,” people who are used to using Lightroom 1 just click into the larger field and start typing. The problem is that the auto-complete function only works with the new entry field.
You can still enter keywords via the larger field, but if you want to use the auto-complete function use the new field expressly designed for that purpose.