Thanks for looking :-)
I was looking at some typical POEdit keyword header value in WordPress plugins and themes - e.g.:
'__;_e;__ngettext:1,2;_n:1,2;__ngettext_noop:1,2;_n_noop:1,2;_c,_nc:4c,1,2;_x:1,2c;_ex:1,2c;_nx:4c,1,2;_nx_noop:4c,1,2;\n';
There's several things wrong here, but the oddity is:
_c,_nc:4c,1,2