[BUG] (BlTouch autoleveling crash into bed)

[Amenia1999]

Bug Description

I followed the Wiki instructions to set up the BLTouch.
Leveling itself works, but when I set a Z-offset of -0.80 (with M851 Z-0.80 + M500), the nozzle goes lower than the bed surface and keeps trying to move down. On -0.79 the filament wont stick, its a bit to high.
At this point, the stepper motors grind loudly.

With -0.79 everything is fine, but with -0.80 the printer crashes into the bed.
It looks like there might be a rounding/limit issue in the firmware.

Steps to Reproduce

1. Flash Release 1.5.4
2. Set BLTouch Z-offset to M851 Z-0.80 and save with M500
3. Home with G28
4. Start print

Expected behavior:
The nozzle should stop correctly at Z0 without pushing into the bed.

Actual behavior:
At offset -0.80, the nozzle tries to move below the bed and the steppers grind.
At offset -0.79, it works fine.

Additional Information

• Printer: Anycubic i3 Mega
• Firmware: Release 1.5.4 witho Driver and Bltouch
• BLTouch is wired correctly and otherwise works as expected
• Sometimes the terminal shows strange values like Count Z:-2147483648 after movements, which looks like an integer display bug. This might be related.