HUGE differential backups

[GDan]

The backup plan is weekly Full backup and two Differential backups per day, and database is aprox. 300Mb.<br>The backup history looks like that:<br><b>Sunday</b>&nbsp;&nbsp;&nbsp;- 19:39 Full (307Mb)<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;- 19:57 Diff (3,1Mb)-it was Sunday evening, nobody works<br><b>Monday</b>&nbsp;&nbsp;&nbsp;- 08:01 Diff (8,4Mb)<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;- 13:01 Diff (44,4Mb) ??? (5 hours - 46Mb)<br><b>Tuesday</b>&nbsp;&nbsp;- 08:01 Diff (74,4Mb)<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;- 13:02 Diff (77,5Mb) ??? (5 hours 3,1Mb - lazy people, huh?)<br><b>Wednesday</b>- 08:01 Diff (295,6Mb) What????<br>After this I make an full backup at 08:47 - it was only 308Mb.<br><font color=red><b>WHY?????</b><br>Please comment.