Steps to reproduce:

• open/create simple project having ClangCodeModel enabled
• inside a function or wherever you like place some code that is illegal [I've just typed some characters to complete them, but canceled the ProposalWidget]
• wait until text is underlined with curly line and a text mark is displayed before the line number
• hit Shift+Del to remove the respective line

Current result:

• cmdline prints sth like

  Could not find mark 0xf8d61e0 on line 195