[gnea/grbl-Mega Issue#35] Rounding error?

Not sure what’s happening but when using multiple tool changes in a program (I do manual changing with probing after using bCNC) it all works ok on first tool change and probe, but on next one I get an error that requested move on Z exceeds machine limits. For some reason, it always tries to move 0.01mm or 0.001mm (not sure now) beyond limit. I have to break program and zero Z every time before tool change.
I asked this on bCNC git, they pointed towards this community, saying that it’s something to do with rounding in grbl. Can anyone help please?