I have a project created in Kdenlive 15.04.2 and now loaded into 15.08.2 -- without any problems with respect to the project itself. MLT is 0.9.8. ffmpeg is recently build from stable git. Kdenlive is built from recent git, branch "Applications/15.08".

My project has an audio track on which (simplified) two audio clips are placed. The first audio clip is a .wav, 48kHz, 32bit float. The second audio clip is a .wav, but 44.1kHz, 32bit float. Now, when I play the project in Kdenlive from start, the first audio clip gets played correctly. When the playhead continues and then reaches the second audio clip, this second audio clip gets played too fast. It sounds as if playing 44.1kHz at 48kHz.

When I stop playing the project, then start again playing from the current position (not from the beginning), then the second audio clip gets played correctly, that is, at the correct sampling rate.

When I render the project, then the audio track is correct; that is, all audio clips get rendered correctly and converted to the project's audio rendering bitrate.

As rendering the project works, I would imagine that this is a problem not in MLT itself, but in the way Kdenlive interacts with MLT during project playback.