Something broke my post

I have weird problem with my WordPress setup (2.2.3). I started to use WordPress couple years a go, but this problem started just in last couple of month. I write a post and publish it, after that I check that everything is ok with that post. I maybe even get some comment’s to that post, everything seems to work ok. But sometimes post just get broken after some time. Sometimes that happens next day, next hour or even after several days.

After some time part of the content gets lost. There is always % in the end of post after that. Usually there is many words lost, even hundreds of them. So I have to keep backup to my computer.

Example:

—

This is my post. Thanks for your time.
This is second line of my post.
Bye.

After some time:

This is my post. Thanks for your time.
This is second line%

—

Any ideas what could be wrong?

Sorry about my english.