Created attachment 168421 [details]
input file a

SUMMARY
Data loss error dialog is displayed when comparing 3 files and the "Align B and C for 3 input files" preference is checked.

STEPS TO REPRODUCE
1. download the 3 input file that are attached. These file will demonstrate the problem.
2. open kdiff3, go into the kdiff3 settings and check the "Align B and C for 3 input files" option in the Diff Settings tab
3. diff the 3 files by running: kdiff3 a b c

OBSERVED RESULT
a Severe Internal Error dialog will pop-up saying:
Data loss error:
If it is reproducible please contact the author."

My removing line 3 from file c the issue will go away. 

EXPECTED RESULT
I expected kdiff3 to open normally and display the differences between the 3 files

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Red Hat Enterprise Linux release 8.9 (Ootpa)
KDE Plasma Version: 
KDE Frameworks Version: 5.96.0
Qt Version: 5.15.3

ADDITIONAL INFORMATION
$ dnf info kdiff3
Installed Packages
Name         : kdiff3
Version      : 1.8.4
Release      : 1.el8
Architecture : x86_64
Size         : 5.8 M
Source       : kdiff3-1.8.4-1.el8.src.rpm
Repository   : @System
From repo    : epel
Summary      : Compare + merge 2 or 3 files or directories
URL          : https://github.com/KDE/kdiff3