Adobe Premiere Elements 11/12 flipped my output MP4 files, How to fix it ?

[AAC]

I spent a whole week to create a short video by APE 11, in which I flipped one video clip horizontally to work with the storyboard.
Everything looks perfect when playback on timeline. However, when output working file to MP4 (1980 x 1080), all images and layout in the MP4 file were all Left/Right flipped. I edited more than 50 video files by APE 11 previously but none of them went wrong like today.
I then tested it again by converting an old working file to MP4 with APE 11, same result, all images flipped.
Later today, I upgraded to APE12 and converted new and old Adobe Premier working files again, no luck, all flipped, including text.

Very frustrated, what's wrong with me ? I recall that I didn't make any setting changed on APE. Only installed one trial version of video editing software yesterday but uninstalled it after finding it's useless.

[newpball]

So it looks fine when you play it on the timeline and only one single clip is flipped but when you export the timelineto a video file all clips are flipped?

I find that hard to believe.

[poisondeathray]

First rule out a playback issue. How are you determining they are "flipped"? What software ? Do other unrelated clips (MP4 and other file types) play normally, or are they "flipped" as well ? Try another media player e.g. VLC, MPCHC, Potplayer, SMPlayer, etc...

Try another export format, like uncompressed AVI , just for a short test to see if that is "flipped" also

[AAC]

I reinstalled everything, and they are back to normal now.
Thanks for all advice.

[budwzr]

So an Adobe Premiere Elements "silent bug" was the perpetrator?

[AAC]

So an Adobe Premiere Elements "silent bug" was the perpetrator?

Could be my computer.....
I downloaded one trial version third party video editing software, hoping to solve the issue but uninstalled it after finding useless....