This issue is intermittent. Changing the output file destination field by hand doesn't seem to freeze the app, but specifically clicking the "Open file dialog" button next to the output file text field in the render window will cause Kdenlive to freeze.

Reproducible: Sometimes

Steps to Reproduce:
1. Open (or create new) project
2. Insert clips in timeline and create edit
3. Click on the "Render" (Export) button in header toolbar, then click the "Open file dialog" button

Actual Results:  
Intermittently works. When it doesn't, Kdenlive freezes and becomes unresponsive

Expected Results:  
Should always open the dialog box so the user can choose where to save render output file.

Using Kdenlive 15.09.0 (kdenlive_15.08.1+git20150922.0224+15.10-0_amd64) on Kubuntu 15.10 x64 beta.