We are looking at this issue. But because of its intermittent nature, we are unable to reproduce the issue.
Can you share the sample files with which you are facing the issue?
Are there any specific softwares installed on your system?
You can mail me the files and information at email@example.com
This is happening to me often. I unchecked ligatures in the character and open the file and there are ligatures in the file. I turn off ligatures and its OK for a while. Then it happens again, I check ligatures in the character panel and it's checked again.