After the errors above are received, the user also has to Clear AP flags in Division Maintenance and the obligation will be back in the stage where it started.

We do not have many instances where this has been reported by clients (only 2 since 2003) and to correct the issue would be fairly destabilizing to the AP module.

A workaround should be attempted to split the obligation in a different way.  Instead of splitting out the negative line, split the obligation for the positive lines and post it.
You will then have 2 obligations which can be edited to correct the negative amount.  You may want to try the procedure in a test division to see what will work best for your organization regarding what detail and distribution lines you will want to split prior to editing.

The same type of error may be generated if a user tries to split an obligation by changing quantities and unit amounts.