Weird extent sizes in locally managed tablespace

I created a tablespace with the following parameters.

extent management local autoallocate
segment space management auto

Under this setting Oracle will extend in increments of 64k, 1m, 8m, and finally 64m based on the size of the segment. I'm seeing a table that was extending 8m at a time, but Oracle threw in a 3m extent and a 5m extent. Can anyone explain this weird behavior?

The tablespace only has 1 datafile and the datafile has never been extended.

extent_id bytes blocks

  97.00     8388608.00        1024.00
  98.00     8388608.00        1024.00
  99.00     8388608.00        1024.00
 100.00     8388608.00        1024.00
 101.00     5242880.00         640.00
 102.00     8388608.00        1024.00
 103.00     5242880.00         640.00
 104.00     8388608.00        1024.00
 105.00     3145728.00         384.00
 106.00     8388608.00        1024.00
 107.00     8388608.00        1024.00