Since version 2.6 MorphOS sends an IDCMP_NEWSIZE message to an application after it called MoveWindow(). No other AmigaOS derivate/clone does this. Is it intended behaviour or a bug?

For PicShow this means the window cannot be moved any more because when it receives IDCMP_NEWSIZE it interrupts the movement and scales the picture to the new window size (which actually hasn't changed).

IMHO IDCMP_NEWSIZE should not be sent to a window if the size was not changed.