@Alexmach: There is a default setting (Indeterminate Media Timebase) in Premiere which assigns a frame rate to an imported image sequence. In this case, it has almost certainly assigned a frame rate of 29.97 (NTSC) instead of what you want, which is 24. Find the setting and change it to 24, and your problem should go away.
Try this: Go to Edit>Preferences>Media... and change the Indeterminate Media Time Base to what you want (23.976 or 24)...problem solved.