Search bug or some limit?

[tflx]

I have 2 links to heroku in a collection. If I do a search for "herok" I get those 2 results returned:
https://api.raindrop.io/rest/v1/raindrops/0?search=[{"key":"word","val":"herok"}]

If I search for "hero" I don't get any items (and no errors):
https://api.raindrop.io/rest/v1/raindrops/0?search=[{"key":"word","val":"hero"}]

If I search for "he" I get one other item in the results, but not the 2 heroku links:
https://api.raindrop.io/rest/v1/raindrops/0?search=[{"key":"word","val":"he"}]
…which indicates that it is not a minimum character search that's the issue.

Do you know what's going on here?