Werner,
Yes autosave seems to be one option. But really it is frustrating to lose all the sheets you are working on in the middle.
Vladimir,
It is fairly random, or at least, I haven't established a causality with any other applications. My workstation has Intel i7 3770 (3.4GHz) processor, 32 GB RAM and Windows 7 64 bit Proofessional OS. Although I must mention that this has started happening more frequently since I upgraded to M030 from M020. Don't know if that is the cause anyway.