This page explains the case when the transaction is flagged as MODIFIED in the evolution node, while there is no change in the analyzed code source.
Technically, transaction status is based on the transaction checksum. In a given snapshot, if a transaction has a different checksum than in the previous snapshot, then it is considered as MODIFIED. Transaction checksum is calculated based on the checksums of the objects inside the transaction.
For more information on checksum value, refer to the following page SQL Queries - CAST Central Base - Queries on objects - How to get the Checksum value of an object