While testing my (rewritten) NVRAM routines, I noticed an odd issue: if the NVRAM is written to starting from a certain address, the WinUAE NVRAM file grows beyond 1024 bytes. More precisely:
1. my tests write 6 bytes at arbirary NVRAM addresses between 0 and 1018;
2. if the address used is between 0 and 1008, the behaviour is normal;
3. starting from address 1009, the NVRAM file grows by address-1008 bytes.
Here is a picture that shows it visually (click to enlarge):
Moreover, the extra bytes get apparently random values: after restarting/resetting UAE and running the same test again, the values change.
If they are of any help, the archive attached here contains the test programs and the corresponding NVRAM files.
I've tested this using the public beta 31 and also the beta 0 2020.03.20 you gave me with the NVRAM debug log enabled.