Duke3D: Another tight vent that can no longer be entered

Yet another edge case, but I'll record it for completeness' sake:

In abcstudios.map (can be found as part of the Urban pack of the Addons Compilation, see https://forums.duke4.net/topic/7640-release-eduke32-addon-compilation/page__view__findpost__p__366218), the following vent could be clipped through prior to r7398 (commit 374bdaaa), but is now blocked off: Similarly, the following vent in the same map also cannot be entered:

Here's the test map to reproduce the problem: another_tight_vent.map