Probably a side effect of the fan fix, I will check it out, thanks for the report.
Heh, you found the only valve in the game that would have this issue.
Sorry. :)
No, thank you, this could have been around for ages before anyone noticed and then it would have been painful to debug.
Apparently a similar thing happens in c2a5, when the dam's grate is almost open.
Would probably check any hold-switches whose targets close back when the button is released.
Nothing extracted yet.
After defeating (or ignoring) the Ichthyosaur, you can't get past the grate blocking further progression because it resets when attempted to raise.