Forget "design flaws". Is the entire Galaxy concep

[montypython]

Transparent Aluminum is supposed to be the material of choice for glass applications in ST, so I think that's what the windows would be.

[Bounty]

Are the observation windows only forcefields, or do they not have some damage feature wherein a metal sheet (or transparent aluminum sheet) will qutomatically close over where the inactive field was during a power failure?

In any sane universe they would, but given that this is Starfleet we're talking about I wouldn't count on it. However if it closes at the same speed it opens any such feature will be no consolation to anyone in the compartment, as they will have long since been sucked out into space.

Windows in Trek are solid. Picard has a reflection in the glass in FC, the dome over the bridge shattered - can't have that with forcefields.

The supposed "window" in FC people keep pointing out wasn't a "window" at all - it's deep inside a service duct and normally sealed off with a metal plate, which suggests it's some sort of entry hatch of umbilical port.