[exim] bad memory reference; pool not found, at gstring_grow…

I'm getting this error panic
"bad memory reference; pool not found, at gstring_grow 1124"

at a acl logwrite in an ${acl expansion in a router

the logwrite is over-size and thus truncated in the debug message

then it crashes.

it seems to happen failry rarely, maybe 1 in 10000 emails on this path.

--
Jasen.