While trying to correctly intonate guitar(which was problematic, you can see my last question why), I noticed a strange thing and I don't really know if it is normal or not. I've searched about it everywhere and found nothing, so I hope you can help me.
I was fretting 12th fret to check my intonation(But it does this not only on 12th fret, even on open string) and was looking at the tuner same time. I felt that I held my guitar in a bad position(it was slipping) and I corrected it and suddenly there was a different reading on my tuner. Then I did this test: I held my guitar in normal position(not classical) and started to angle it towards the floor while plucking the string and the note was getting flatter. Then I did the same but tilted it towards the ceiling and note got sharper. So my tuning depends on the position the guitar is held and even a little tilt changes it.
What can be cause of this and is it just my problem or guitars do that in general? (I don't have any other electrics to test this)
Edit: I made a video demonstration here (youtube)