Thanks hcorion, I went and got the latest version of Source Code Pro fonts and installed them on my system, and indeed the problem went away. So that's great for me, but others will likely have this same problem and not know what to do.
TBH, I'm not sure how the Source Code Pro fonts ended up on my system in the first place. I don't know if it's a Visual Studio thing or what (seems like they used Consolas the last time I checked).
