Problem with standard regex

[Kornel Benko]

Given the string
	t = "\foreignlanguage{russian}{\texttt{\label}"
and trying to use
	"regex_replace(t, t,
	"\\\\(emph|noun|text(bf|sl|sf|it|tt)|(u|uu)line|(s|x)out|uwave)(\\{(\\{\\})?\\})+",
	"")
leads to regex-exception.
Anything other than "\label" works. (e.g. "\xyzzy" or "\lxabel", or "\labelx")

Does anyone know, what's going on here?
(It does not even depend on "\texttt", because already
	t = "\foreignlanguage{russian}{\label"
leads to the exception.

	Kornel
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