mvexpand gives "mvexpand output will be truncated due to excessive memory usage"

I give my splunk 50GB Mem with max_mem_usage_mb = 50480 in the limits.conf but splunk 5.0.3 gives me a "mvexpand output will be truncated due to excessive memory usage". THe job inspector shows that the incoming data are a few 10 MB.

Miss I a hidden config-option?

Best regards Marco