For those interested on this topic, I got the explanation, which is at
It turns out that if one uses the Standard C++ Library as well, then MSVC will link against MSVCP*.DLL, too. Since there's no replacement for this file by Cycling '74, both the Cycling '74 CRT (for the CRT) and the MSVCP (for the C++RT) would be linked.
The weirdness is that I've never had any linkage problems while I was using MSVC 2008, although the codebase was more or less the same (my guess is that most of the people using my externals probably had the 2008 versions of MS DLLs already installed on their computers).
Hope this would help others,
Ádám