Looks like expectk doesn't source local and global rc files. It happens both for CVS (with patch from 2585764, otherwise it doesn't start at all) and for older releases (e.g. 5.43.0). expectk -help returns the following among other info:
-norc: Don't read ~/.expect.rc
-NORC: Don't read system-wide expect.rc
so, rc files should be sources.
The attached patch moves my_rc and sys_rc definitions up and adds call to exp_interpret_rcfiles(interp,my_rc,sys_rc) which seems to fix the bug. The variables are modified in Tk_Init2() during command line parsing. Note that the patch from 2585764 is still necessary for expectk to run.