When you have an issue number, like JIRA-12345, it doesn't work to use the underscore to italicize the text:

This:

_After JRA-11564_ was solved... something happened.

Becomes this:

After JRA-11564 was solved... something happened.

This is true for all inline markup: italics (underscores), bold (asterisks), underline (pluses), strikethrough (dashes).

This is a workaround:

_After_ _JRA-11564_ was solved... something happened.

which becomes:

After JRA-11564 was solved... something happened.