Using the latest version of Spotify (Free) on an iPhone 4 with iOS 7.1. There are a couple of annoying bugs that I can reproduce without fail everytime. 

The first bug has to do with shuffling. Every couple of songs or so, if I hear a song I don't like and want to skip to the next one, it'll skip 2 tracks instead of one. So for example, I'm listening to track A. I don't like track A, so I skip to track B: instead of the Spotify app playing track B, it'll skip right away to track C. Very frustrating, especially as there is a skip limit per hour which gets screwed up through no fault of my own. 

I'm listening to track A, I lock my phone, and it ends. Track B is now playing in my speakers, but track A still shows up on my lock screen. If at this point, I don't like the song I'm hearing and want to switch, I usually unlock the app and swipe to the next song I want to hear. However, if the track A is still being displayed on my screen while track B is playing in my speakers, unlocking my phone and opening the app will cause the app to crash 100% of the time, without fail.