addcol:A colA:=[substitute:a.b.c.d,c,_]
a0b0_0d
addcol:A colA:=[substitute:"a.b.c.d","c","_"]
a0b0_0d
The dot is seen as a number (0). Not only in the text field, but also in the replace field.
More curious:
addcol:A colA:=[substitute:0.b.c.d,.,_]
0_b_c_d
(the zero is not replaced)
Didn't test the replace (preprocessor) function and family (substr, ..)
BTW: To make sure the dot was numerical, I checked in 1386a: "." was replaced with "0,0" (comma is decimal separator here)