Build 5185: AVI output displays twice FPS

[meRobs]

When converting to AVI with Xvid/Xvidcore or H.264/x264 the output file displays twice the set frame rate.
For example, if the PAL values are set, ie 25 FPS, the Properties panel shows "Frame Rate: 50 fps" and MediaInfo gives "Frame rate = 50 fps and Original frame rate = 25 fps".
Similarly, if NTSC (29.97 fps) is set the output is displayed as twice the correct rate.
Yet, the files play correctly.

I checked the same conversions in builds 5150, 5175 and 5180. They give the correct values and the files are otherwise the same. They play as for 5185.

Hence, it looks as if MediaCoder 5185 (or its versions of Xvidcore and x264?) writes the incorrect value to the File Header!
Another clue is that Xvid/FFmpeg does not give the error!