@renluop and @VDSL2: I've now uncovered the source of the floating point errors. It has nothing to do with the graph timing, it's related to automatic snapshots, and one snapshot in particular (by default the snapshot timing is the same as the graph timing, which is why it seemed to relate to that). The one snapshot which is causing the problem is the average errors text page. If you disable this snapshot you should find that the floating point errors are no more.
I'll incorporate a proper solution in the next release, but until then please disable that snapshot option.