Some Unicode-Characters aren't rendered and confuse cursor

Description of the problem or steps to reproduce

Use this input (either as a file or just paste) and play around, the first ess-zet will be rendered but not as an umlaut (and just takes the space of 2 characters), the second is not rendered not at all but also takes 2 characters, if a character is following the second (big) ess-zet with diacretics it will be displayed but the following character swallowed.

ß̈ ẞ̈
ß̈ ẞ̈|

Output is basically:

ß␣␣␣\n
ß␣␣ß␣␣

where ␣ signify space. The space following the ess-zets is each the part of the multi-byte sequence denoting the points on the character, so one can delete them and have "normal" ess-zet instead.

Specifications

Arch-Linux amd64, most recent micro version

Tested on:

$ ./bin/micro --version
Version: 1.4.1-27
Commit hash: 6d2cbb6
Compiled on February 21, 2018

and

$ micro --version
Version: 1.4.0
Commit hash: af520cf
Compiled on January 26, 2018

Commit hash: 6d2cbb6 and even since at least af520cf
OS: Linux 4.15.3-2-ARCH
Terminal: Konsole, kitty Iosevka Font. Alacritty does render the glyphs badly.

Reproduce the Unicode input with ./bin/micro and compare the reported rendering and cursor behavior across the listed terminals. Trace the terminal rendering and cursor-handling entry points, then verify that combining diacritics on both ess-zet forms render correctly without consuming adjacent characters.