Warning while testing specs on postgres: there is no transaction in progress

For each step of test occurs 2 lines:

WARNING:  there is already a transaction in progress
NOTICE:  there is no transaction in progress

With Spork lines following triples:

NOTICE:  there is no transaction in progress
NOTICE:  there is no transaction in progress
NOTICE:  there is no transaction in progress
WARNING:  there is already a transaction in progress
WARNING:  there is already a transaction in progress
WARNING:  there is already a transaction in progress

I don't know maybe it's important, just warned. GemFile:

group :test do
  gem 'rspec-rails'
  gem 'factory_girl_rails'
  gem 'spork-rails'
  gem 'capybara'
  gem 'database_cleaner'
end

all customized, so there is no need for develop group, and it not helps anyway. this is spec_helper.I found, that it is PostgreSQL feature, but I could not find how to fix it. I will be grateful for the assistance