Create a new screen, set its name to "test <emoticon> screen".
Notice how the name is cut to be "test".

Create a new screen, set its name to "test <emoticon> screen".
Notice how it is possible to create multiple screens with identical names this way.

Similarly, edit a template and set its description to "test <emoticon> desc". After saving, notice that the description is cut to be "test ".

While not tested, this problem also likely present in other fields (perhaps graph and other names that are not more restricted, all description fields etc).

While behaviour might be different with other databases and https://stackoverflow.com/questions/39463134/how-to-store-emoji-character-in-mysql-database might help with the MySQL family, it might be more reasonable to limit the allowed characters. If this is done, documentation has to be updated for all affected fields. In any case, limiting allowed characters is likely the only solution before 4.4, as emoticon support would require DB changes.

Note that emoticon support was asked for in ZBXNEXT-3238.