Help: DW destroys PHP code

Hi,

DW started las night to destroy my php-code. It begins to rewrite characters
like > < = to their ascii codes.

Code like $i > $n becomes $i %3E $n

After saving the file the modified code is written to file. So it is not only a
problem of displaying.

At the next loading of the file I get $i %253E $n.

Code rewriting for URLs is off.

Any idea?