Repro steps:

(in a creative superflat world, for example)

set down a piece of glass
drop an item on top of the glass (e.g. wool block)
take a flint and steel, try to light the top surface of the glass a few times

item (wool block) disappears from client view, however if you walk over on top of the glass, you can still pick it up. e.g. item has become invisible