Found the bug in Geany editor with underscores - they were invisible. Default font is Monospace.
For example the text "here_should_be_underscore", displays the same as "here should be underscore". but when copying from Geany to clipboard, the underscores stay there as they should. It's something wrong with displaying.
There is workaround for this issue.
Check the line_height settings in "Tools" > "Configuration Files" > "filetypes.common". Check the settings of [styling] section. It should have those values, if not - add it there:
Results will be enabled right after saving the file. Check screenshots.
Have a nice day!