I've noticed this before, and today was confused by it again.

After clicking 'New Posts'
16 were shown followed by the message:
Results 1 to 16 of 25
There were no next page buttons to see any more.

After reading six of the threads I tried the 'New Posts' again
This time 10 threads were shown but followed by the misleading message,
Results 1 to 10 of 13

Are these anomalies just there to mess with my brain, are secret threads being kept from me, or is this a bug in the forum software that can't count properly?