This can occur when the target segment contains a „tag“ (or what CT considers as a tag), e.g.
I really needed some time to understand the problem, as the segment did not contain any "real" tag (marked by a red number).
Other users might get driven (more) nuts by this.
Technically, these are tags too so it does not hurt to check such space inconsistencies at them. The reason for including the QA check for non-CafeTran tags are the projects coming from other CAT tools with unknown tags. The benefit of including them is greater then solving your issue by excluding them.