Changes saved or applied to current source code

What causes this issue?

When you carry out a global replace in the Editor in change mode, the
current source text is passed to the replace module. Other source text
is read from the database.
The Save function in the hit list copies the changes from the hit list
to the source text in the database, apart from the current source text,
which is returned with its changes to the editor which called the
function. You must save this changed source text in the editor to save
it to the database.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.