Copying and pasting the degree symbol into the abstract field seems to cause the following error in IE, but not in FF. Software error: Can't call method "fields" on an undefined value at /home/koha/kohaclone/C4/Biblio.pm line 2101.
I couldn't reproduce this in IE8 on Windows 7. I added a degree symbol (Unicode character U+00B0, Windows keystroke Alt+0176) to 5xx fields and was able to save the record without error.
This could be an issue with Unicode normalization... NFC v. NFD...
I did the same as Owen and no problems saving. Maybe some NFC work done after 2012-06-29 has fixed it. I Used IE 8 on Win7.
Two attempts to reproduce this bug failed. I'm going to consider this fixed. Please re-open if you can provide more details about how to reproduce.