Although this is not exactly the same issue - something that might be relevant is this:
@sam did put a fix in for something similar to this sort of thing back in July 2016:
https://github.com/discourse/discourse/commit/12ecf8624a97c3d33aaa3cd56851b5f1ca347c90#diff-995f4013dde76fb0460ecdb36fa20d53
Where the last word wasn’t searchable.
Although the file app/models/search_observer.rb doesn’t seem to exist in the current version of the code I assume those fixes are still in there somewhere…
Because the tests still exist for it:
https://github.com/discourse/discourse/blob/master/spec/components/search_spec.rb#L701-L704
But as I said before - perhaps a slightly different issue.
EDIT: found the current relevant code: