Sounds like a request for functionality that we never had (natural language queries in window title search while in overview). Marking as FR and removing a milestone - this is not something we can introduce so early. Also I don't think this falls under MD so removing MD label.

Out of interest, what should a user type there to get any results? 

I misunderstood the repro steps. I thought it was literally "Files or Downloads". So this is simply about leading space in the search query. why would you expect space to do do anything other than literally mean ' ' or be sometimes ignored?

For #2 - A user would need to erase the space and then type any substring of a window caption. If a window caption contains space those windows will be selected (e.g. "Chrome - New Tab" or "Chromebook Recovery").

Ah, I assumed pressing space brought up the search bar. Didn't realise typing anything brought it up!

#4, would you think this is a popular confusion? If it is we might want to do something about it still but I think we can WontFix this one.

Well, I actually only found the search bar because I tried to press space to open the selected window. It's a pretty hard to discover feature without a prompt of any kind 

This is a power user feature, so we don't prompt users to use it.

I do think we can improve the search feature though -- stripping whitespace from the start/end of the query would be nice, as would searching over all tabs within browser windows instead of just the currently selected one.

Adding to MD CrOS hotlist so we can see about making some of these improvements after MD Shelf/System Menu are finished.

#5 - here is an example of "popular confusion"

There is a recent post on CBC from a user who inadvertently discovered this feature. Improvements, documentation, and UI prompting seem to be warranted.

https://productforums.google.com/forum/#!topic/chromebook-central/5VWZuCpCJ54;context-place=forum/chromebook-central

#CBC-RS/TC-watchlist

Maybe briefly show and animate away the search box when the overview is initially shown?

I agree with dhaddock@ that it's somewhat confusing. Exploring how we can signal better to users the purpose of this search box - potentially listing instructions in search box. 

(Bulk Edit) Adding the new conops Chrome OS hotlist to all open issues with the "#CBC-RS/TC-watchlist" tag, our former tracking tag.