Kerbal Space Program

'Standard' parachutes (eg, the Mk16) have a 0.04 minimum pressure limit for activation in the VAB; you can't set it any lower. However, in flight you can reduce this threshold to 0.01 atm.

Similarly, drogue parachutes (eg, the Mk12-R) have a 0.02 minimum pressure limit, but also can be reduced to 0.01 when in flight.

I'm not entirely sure what the intended behavior is, but I find it difficult to imagine that this is it. This issue has been around for a long time; I have a vague recollection of submitting a bug to this tracker back during the 1.1 public beta, though I can't seem to find it.

Steps to reproduce:
1. Put a Mk16 Parachute on a Mk1 Command Pod in the VAB.
2. Attempt to reduce the parachute's Min Pressure to 0.01. Note that it does not work; 0.04 is as low as it will go.
3. Launch the craft.
4. Attempt to reduce the parachute's Min Pressure to 0.01. Note that it does work.