Games with presets crashing

[Somechump]

I have just modded my Dreamcast with a piggyback bios and IDE HDD.
I have flashed the bios with "boot_loader_unlock_G1_IGR_dbs.bios"
and installed the DS folder to the root of the HDD with the latest DS_CORE.BIN.

Everything seems to work fine except when loading a game (optimized GDI) that has a preset, the DC will reset.
For a game without a preset, when I select the Disk.gdi file the box art will show up, press A and the game loads. If I then save a preset for the same game, when I select the Disk.gdi file, the DC will display some stack dumps and reset, this is before the cover art shows.
Deleting the preset will again let the game work.

How do I get presets to work correctly?