#15 ctags: Warning: f.q:59: null expansion of name pattern "\1

[prodrive11]

Hi,
I have problem with ctags when trying to parse user-defined language.
I've tried different flags: b,e for regex. My definition of tag is:

--regex-q=/^[ \t]*[^[:space:]]*[:space:]*:[:space:]*{/\l/f,function/b

I've an error:
ctags: Warning: f.q:59: null expansion of name pattern "\1"

When I replace \1 with anything else:
I've correct parsing.
asdf function 212 f.q .ras.init:{