Simplenote auth fails because of incorrect base64 encoding

Today I bought CintaNotes and found that it doesn't sync with Simplenote. Short investigation showed that it generates incorrect base64 string for /api/login call to Simplenote API with my credentials. When I changed my password, everything works fine.

My password was something like this:

ab_cdefgh0ijklmn 

(with underscore and zero)

if you need real examples of input/output, drop a mail to andrei.palchys [at] gmail.com