ROOT.TFileMerger missing events when using SetFastMethod(True)

I have met an issue with the ROOT.TFileMerger.
When I set SetFastMethod(True) to merge several files together, it collects only half of the events.
When I use hadd instead, it will show full events(93 events). And when I turn off SetFastMethod to be false, ROOT.TFileMerger collects full events as well.

So could anyone take a look what happened on the SetFastMethod(True)? Actually hard to detect this kind issue and may cause unrealized problems when doing MC/data comparison.

Many thanks!

ROOT Version: ROOT 6.10/04
Platform: Not Provided
Compiler: Not Provided

If you have two files we could use to reproduce the problem, please file a JIRA ticket. I’ve looked at the code, but couldn’t find any obvious place where we could have a bug.

This is a surprising report. hadd uses TFileMerger with (by default) SetFastMethod(True) and thus the 2 things you tried should have been identical. Can you please provide a reproducer so we can resolve this?

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