Steps to replicate the issue (include links if applicable):
When creating string after other string, I:

• created a new function
• entered a label and description
• entered strafter | substring-after into the aliases field (guessing that | would be the separator as it is in Wikibase)
• submitted the form

What happens?:
The function was created without any aliases; I only noticed this today, two days later. I would have needed to press Enter after adding an alias (and do that twice, for the two aliases) to actually add it.

What should have happened instead?:
The alias(es) should have been added, or at least there should have been some warning / indication about the aliases input being incomplete, rather than it being silently ignored. The equivalent OOUI component automatically adds an “element” / “chip” / whatever when the input loses focus; in this case, that wouldn’t have been 100% correct (unless it also split on the | character), but at least it would have shown me that there was a “chip”-like state at all, and then I could have fixed it.