I believe I ran into this issue today. After talking with a support agent, we found out that the resolution in the Sequence settings was @ 720p and my footage was @1080p. The picture would be fine after the stabilization process but I would get a sizeable black bar at the bottom of the screen after I rendered the video.
Bottom line: Make sure that your sequence resolution matches the resolution of your footage or is at least larger than your footage resolution.
To give more background. I was using PluralEyes to sync the the audio and video. I haven't figured it out yet but when I imported the .XML into Premiere Pro CS6, the sequence resolution would be set to 720p. I fixed this by creating another sequence in the project with the proper resolution and basically copied and pasted the footage from the imported sequence into to new sequence.
Having the same issue as roque32 an OP.
Original GoPro footage converted and exported with CineForm codec: 1920x1080
Sequence settings for Premiere are 1920x1080 (both 29,97 frames/second)
After applying the Warp Stabilizer, realtime playback is smooth an without black edges or bars.
But after rendering a black horizontal bar at the bottom of the clip appears.
To make sure my sequence is right i've created the sequence from clip, but I can't seem to get a render without black bar.
Any suggestions on how to approach this? By realtime playback the video looks great, if only I could get it to render right..