Which version of Overachiever are you using?
0.64

Can ClearFocus() be used please to remove the blinking cursor from the editboxes when clicking the search button or hitting enter to search, like other blizzard windows can do? I agree this behavior on its own seems minor and not worth worrying about, but it leads to something that is troublesome when the search can be so slow and any mistake in the search locks up the game searching a lot.

The major problem is when the search is over after that long wait and enter is accidentally hit again when I was trying to type somewhere else. It starts searching from scratch again for a long time unnecessarily.

The minor problem is when the search is over and I hit slash to type in chat. It does not go to chat and still stays in achiever messing up the search.

For example, to help I had to edit,
Overachiever_Tabs\Search.lua
local function beginSearch()
  EditName:ClearFocus() -- added
  EditDesc:ClearFocus() -- added
  EditCriteria:ClearFocus() -- added
  EditReward:ClearFocus() -- added
  EditAny:ClearFocus() -- added
  ...
local function createEditBox(name, labeltext, obj, x, y)
  --editbox:HookScript("OnEditFocusGained", focusEditBox) -- commented out
  ...

Thanks.