Weird behavior on continued string literals

On latest master (58890f2b), the following reproducer produces a bad-looking output:

astyle --indent=force-tab=8 <<EOF
#include "dummy.h"

int function()
{
	fprintf(stderr,
		"multi\\n"
		"line\\n"
		"literal\\n");
}
EOF

The output is:

#include "dummy.h"

int function()
{
	fprintf(stderr,
	"multi\n"
	"line\n"
	"literal\n");
}

Curiously, when I remove the #include "dummy.h" line, it leaves the string literal alone:

int function()
{
	fprintf(stderr,
		"multi\n"
		"line\n"
		"literal\n");
}

This seems to have broken somewhere between 3.6.3 and 3.6.4.