The following markup renders in an unexpected manner:

{{-this should not be stroked out}} I would expect this to be stroked out as well if the previous is {{--this needs two dashes}}
{{+this should not be underlined}} I would expect this to be underlined as well if the previous is {{++this needs two plusses}}
{{*this should not be strong}} I would expect this to be strong as well if the previous is {{**this needs two astracies}}
{{_this should not have emphasis}} I would expect this to have emphasis as well if the previous does {{__this needs two underlines}}
{{??this should not be cited}} I would expect this to be cited as well if the previous is {{???this needs three question marks}}
{{^this should not be superscript}} I would expect this to be superscript as well if the previous is {{^^this needs a bunch of caret}}
{{~this should not be subscript}} I would expect this to be subscript as well if the previous is {{~~this needs a two of tilde(s?)}}

Assuming that JIRA suffers from the same problem:
this should not be stroked out I would expect this to be stroked out as well if the previous is -this needs two dashes
this should not be underlined I would expect this to be underlined as well if the previous is +this needs two plusses
this should not be strong I would expect this to be strong as well if the previous is *this needs two astracies
this should not have emphasis I would expect this to have emphasis as well if the previous does _this needs two underlines
this should not be cited I would expect this to be cited as well if the previous is ?this needs three question marks
^{this should not be superscript} I would expect this to be superscript as well if the previous is ^this needs a bunch of caret
_{this should not be subscript} I would expect this to be subscript as well if the previous is ~this needs a two of tilde(s?)

And a screenshot, for when/if it is fixed:

Enjoy™