We assume the following Segment:
Source: "TermA_transFound TermA_transNotFound"
Target: "TermA WrongTermA"

The second TermA in source is transNotFound, since the TermA is twice in source, but once in target.
If we correct target now to "TermA TermA" both terms in source are set to transFound. Until here its all correct.

This circumstance is not recognized by the algorithm to identify the terms for the transit info field on export (the corrected terms are added to the info field).
Problem is, that one correct TermA pair was already in the segment, so the second, duplicated and corrected term is not recognized any more.
Problem is the construct, which does not imply different counts only existance:
if(empty($foundAtImport) && !empty($foundAtExport)) {

The client is informed about this bug, but currently this is not critical.