running on Ubuntu lucid, not sure which version of kdenlive (don't have computer with me to check it) but it was recently installed so its probably 0.7.6 or 0.7.7.

I set keyframes into the audio track to attempt to mute a particular section, keyframe controls show up and work as expected, but when I play the video in the project monitor there is no change to the audio levels. Tried it with combined video/audio track and with separate tracks, same result. Do I need to render or something to enable the keyframe effects, or is this a bug that I should report?

Please report your kdenlive and mlt versions.

When it wasn't working I was using kdenlive 0.7.7, but didn't check the version of mlt. The kdenlive configuration command didn't complain about anything so I assume I had the latest version of mlt as well, but I didn't check the version number for sure.

I reinstalled everything from scratch and now it works OK.

In my previous attempt I originally had an earlier version of kdenlive installed which eventually got updated to 0.7.7. I removed everything and reinstalled Ubuntu Lucid without any previous version of kdenlive on the system, then installed kdenlive for the first time directly to 0.7.7 after reinstalling Lucid.