हम हवाई जहाज़ उड़ाने वाले, फिर भी फ़िदा हैं, पटरी में दौड़ने वालों पे. - SK Mangla

This is a situation where the PNR has not been confirmed in either the same Class or for the same Leg (journey slot from booked boarding point to destination point).
To explain:
a 2AC ticket is confirmed for 3AC,
a ticket from station C to F is confirmed for station D to F OR SO.
When...
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you see such PNR, one more PNR may be reflected (check at indianrail.gov.in) which will show the exact status on charting.
This has its own limitations and complications which may be discussed at length if you find some of above situation.
This normally happens when you are counted as VIP but desired accommodation is not available as it is.