In my opened PL/SQL Dev i open the find dialog (CTRL-F) and enter the searched string, after that, i hit the search button. The following occurencies i search via F4 (search next).
So looks after a "normal" search.
I tried out the global search bar, but it's the same...
Hm, i remember, the earlier this morning the buttons were active and function as well, but now they are greyed out again ?