Markup is active even when turned off

[LouisStrous]

I have "Format messages with markup" turned off in Preferences / Advanced / Input options, but when I type _X_Y into a new Slack message then it automatically changes to XY with the X part in an italic font, so markup is active after all. I wanted to include in a Slack message a C++ macro name with that pattern, but the automatic removal of the underscores mangles that name.

Production 4.42.117 64-bit