riot-rte.md

Two input strings:

!test1 one_two three_four five
!test2 one\_two three\_four five

With the RTE off, these get sent as

"content": {
  "body": "!test1 one_two three_four five",
  "msgtype": "m.text"
}

"content": {
  "body": "!test2 one\\_two three\\_four five",
  "msgtype": "m.text",
  "formatted_body": "!test2 one_two three_four five",
  "format": "org.matrix.custom.html"
}

With it on, as

"content": {
  "body": "!test1 one_two three_four five",
  "msgtype": "m.text",
  "formatted_body": "!test3 one_two three_four five<br />",
  "format": "org.matrix.custom.html"
},

"content": {
  "body": "!test2 one\\_two three\\_four five",
  "msgtype": "m.text",
  "formatted_body": "!test4 one_two three_four five<br />",
  "format": "org.matrix.custom.html"
},

FWIW, github renders them this way:

!test1 one_two three_four five

!test2 one_two three_four five

And I'd expect Riot to consistently pick the first or third renderings.