Yes, you're correct, Aaron, thanks. Apparently the secondary substitutions only get processed after all the questions are asked and the template is written out to the temp buffer. So the backslash has to be escaped to survive the first round of substitutions.
I kind of feel that this should be stated more explicitly in the manual. IN BOLD TYPE.
maabaum
You need to escape the backslash inside the string, I think. "\1" is
interpreted as a string consisting of one character, the ASCII character
with hex code 0x01, which happens to be C-a. "\\1" is a 2-character
string: backslash, then one.
--
Aaron Ecay