REQUIREMENT: The following format is required to render a 320x240 video to be compatible with a hardware device:
General
Format: MPEG-4
Format profile: Base Media / Version 2
Codec ID: mp42
Video
ID: 2
Format: AVC
Format/Info: Advanced Video Codec
Format profile: Baseline@L1.3
PROBLEM: Although AME H.264 uses the mp42 codec at higher resolutions, it switches to m4v when exporting 320x240 (as per MediaInfo). A series of encoding tests showed the following for the AME H.264 and MPEG4 export settings:
H.264: m4v codec when exporting Baseline Profile 320x240
H.264: mp42 codec when exporting Baseline Profile 480x360, 640x480, 1280x720
MPEG4: mp42 codec when exporting Advanced Simple Profile 320x240
QUESTION: Is there an AME setting that uses the mp42 codec to export a Baseline Profile 320x240 video?
SPECS: CS6 Premiere Pro v6.0.3, AME v6.0.3.1 (64-bit) on a Win7-64 system
Looks like a bug to me, and you're up to date so an upgrade won't help.
There is no reason why the container should change based on the stream information change.
I know x264pro gets it right.