Ok this is a bit of an extreme edge case but I found it anyway :D
If "Insert _ after m and Shift" is enabled, while holding shift and clicking the mouse to select a region, if the location you click is after a single identifier 'm', it will replace the selection you just made with an underscore.
Say you have this line of code, where the caret is indicated by the |
foo(a, b, m, something|);
And then you hold shift and mouseclick to behind the m, like so:
foo(a, b, m|, something);
Visual Studio will then select the ", something" part as expected, but because you're holding shift and you're behind an 'm', Visual Assist will then insert an underscore, overwriting the selection. Result:
foo(a, b, m_);