When specifying pause time using MaxGCPauseMillis/GCPauseTimeInterval the GCTimeRatio flag is not updated to reflect that ratio.

This means that since G1 only uses GCTimeRatio to determine when to expand the heap, if you give more lenient pause time goals (e.g. 30/50 pause time goals), G1 will expand the heap very aggressively (because 30/50 corresponds to a GCTimeRatio of ~0.7 instead of the default value of 5).