'For what its worth' you say.. ! Its worth heaps !! ALL my wierdness has disappeared. Thankyou so, so much.

The example program I provided was taken from a much larger project that has been working for YEARS and yet only recently did this error reveal itself in dozens of mysterious ways - the tooltip being the easiest to replicate.

All my modes of failure inevitably crashed somewhere in X (typially XSetCommand but elsewhere in X too) which I've just realised recently are passed argc and argv. When I read your mention or argc, I just knew it was likely to work !

RTFMC(arefully).

Regards and thanks again,
John