When I search for certain stock symbols or usernames, the search api will ignore the count param when the result_type is set to mixed, ie:
https://api.twitter.com/1.1/search/tweets.json?q=%23fb&result_type=mixed&count=5 (returns ~20 results)
If I change the result_type to recent, https://api.twitter.com/1.1/search/tweets.json?q=%23fb&result_type=recent&count=5, I get 5 results as expected.