Daylight sensor outputs inverted signal when under large overhang

When a daylight sensor is placed under a large overhang, It would be expected to not output any signal ever, because it doesn't get any daylight. However, instead, it outputs a signal at night, and doesn't during day.

Expected behavior:
Daylight sensor under large overhang would not output signal

Observed behavior:
Daylight sensor under large overhang outputs signal at night

Steps to replicate:
1. Place daylight sensor on ground and put redstone lamp next to it
2. build large overhang about 10-15 blocks above sensor
3. set time to midnight
4. observe as it outputs a signal

can be seen at http://www.youtube.com/watch?v=S7wSbiBMbto#t=19m15s