1. Start a mission on the ground before takeoff.
2. Click the DN LOCK REL button.
3. Raise the LG handle to UP position.
4. There will be a short beep and your aircraft will sink halfway to the runway.
5. No other damage is indicated. No caution or warning lights.
IRL, the mass of the aircraft will prevent the landing gears from collapsing.
If the landing gear collapses, the aircraft should be resting on its air intake and fins, not halfway into the ground...
EDIT: After checking -1:
So the LG will collapse as it happens now.
But the bug remains the same, aircraft should not sink into the ground.