Strange behaviour of the filesystem on FreeBSD-5.5

[Илья]

Hello.
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I have a trouble with /var filesystem on FreeBSD 5.5-RELEASE-p20 (upgraded from 5.2 to 5.3, and then to 5.5 some days ago):
'df -h' shows:
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ad0s1d    248M    138M     90M    61%    /var
'du -s /var' shows:
 28M    /var
I'm sure, that there can not be 62Mb of technical info on such small partition. So, probably there is a bug in soft-updates, or some another thing, that i can't understand. Free space on /var reduces with time, and after three days there are no free inodes. But after i reboot my machine (and background fsck makes it's job), things are good again, du and df are in agreement about sizes of filesystems.
Also i tried to verify, that there are no files, which are deleted, but still occupy place in filesystem (i.e., when some process still use it's filehandle). The output of 'lsof +D /var' shows *only* existent files on /var filesystem.
Can anybody, please, give me some advice about how to fix this VERY annoying problem, since this FreeBSD box is our enterprise's router, and i sometimes must go to office and reboot it even on holidays. Maybe, reinstalling everything from scratch would be the simplest thing to do, but i still hope, that somebody can tell me how to fix everything 'in place'.
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Ilya.