Steps to reproduce: Open new file in Kate. Type:[enter][enter]a Press Ctrl-R, use "Escape sequences" mode. Find "\na". Click "Find All" or "Replace All" ("0 matches found", "0 replacements made") Similarly, "\n\na" is not found in "\n\n\na". 17.08.02 on Arch 64-bit. Also 3.14.13 on Kubuntu 32-bit.
This is fixed for KDE Frameworks 5.50, see bug #381080. *** This bug has been marked as a duplicate of bug 381080 ***