GNU Make version 3.79.1 bug

[Michael S. Tsirkin]

Hello!
The following test demonstates a problem in Gnu make 3.79.1
It is a combination of recursive make, overriding variables
for targets and += operator.

does someone have fix/work-around for this?
thanks,
MST

/tmp>cat make.bug
var = 1
export var
%:
        $(MAKE) -f test.bug
x: var += a

/tmp>cat test.bug
all:
        echo $(var)
/tmp>make -f make.bug  x
make -f test.bug
make: expand.c:489: allocated_variable_append: Assertion 
`current_variable_set_list->next != 0' failed.
Abort
Exit 134
/tmp>make --ver
GNU Make version 3.79.1, by Richard Stallman and Roland McGrath.
Built for i586-mandrake-linux-gnu
Copyright (C) 1988, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 2000
        Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.

Report bugs to <address@hidden>.