Pressure Plates are Thick in 3rd Person

Pressure plates are that thick normally.

When you place them they rest halfway into the block, giving them the appearance that they are shorter.

I thought that was when you step on them or put something heavy enough on them.

Confirmed. The model when held in the hand is a four-pixel-thick plate. On the ground it's one pixel and only 0.5 pixels when stepped on.

Still a concern in 1.7.5 and 1.8

Fixed in 10a

Not fixed in 10c, due to MC-50309

IMO that looks quite intended, since the held item, the inventory item and the dropped item are absolutely identical in thickness.

Confirmed for 14w11b

Confirmed for 14w21b.

Confirmed for 14w25b.