Assuming you are using Microsoft Project, take a look at your Calculation options in File > Options > Advanced. At the bottom of the Advanced page, there are options for how Project deals with the % complete and the status date. Those options will move tasks around based upon the status date and the % complete.
For example: you have a 5 day duration task that is scheduled to start on Monday and finish on Friday. Your status date is Tuesday evening. In the options you have selected the following:
- Move start of remaining parts before status date forward to the status date
- And move end of completed parts forward to the status date
According to the original plan you should be 40% complete (2 out of 5 days) by Tuesday evening. You enter 25% complete for the task. Project will move the start of the task to Monday afternoon so the 25% (1.25 days actual duration) aligns with Tuesday evening. The finish date will be extended to the following Monday so the remaining 75% (3.75 days remaining duration) begins after the status date.
for an in-depth discussion of how the status date and tracking changes schedules. If you don't want Project to reschedule the remaining duration leave all the options unchecked.