"Enable In-Topic Searching" is broken

[aliceif]

I have "Enable In-Topic Searching" activated in my settings.
Hitting Ctrl+F in a topic opens the search box in the top bar with the content
in:topic-12345 (or whatever the topic number is)
with the cursor right in front of that and no space in between (bug 1).

So I hit End and append "test", resulting in in:topic-12345 test.

Then I hit return and this toaster appears:

No search happens.