Since it is crashing, the database server should be generating dumps. Do try submitting those dumps using `dbsupport -sa`. With those in hand you should be working directly with support to investigate thie further. It does sound like you are close to creating a test case to show this issue happening. That could go a long way to determining the fault.
Is there still an indication that the temporary files are involved? {You have not provided any evidence of that yet} If so, have you tried moving the location where the SQL Anywhere temp files are stored;using the SATMP environment variable or the -dt switch. It is possible there is nothing wrong with the main database files or the media they are stored on. That could explain why validation and rebuilding the database is not finding any issues.
