Jet engine discriminates against modular missiles, apparently

[Joey-Destroyah]

Describe the bug
I am making a modular missile with a RAPIER. Unfortunately, the RAPIER says "nuh uh" and refuses to ignite. Or rather, it maliciously complies, producing 0 thrust

To Reproduce
Please provide the steps to reproduce the behavior:

Make a missile with a RAPIER in it (may also work with any jet engine).
Launch it.
See that your engine mysteriously fails

Expected behavior
Proper function of the cruise stage

Logs
Please attach your <KSP Directory>/KSP.log file.

Screenshots
If applicable, add screenshots to help explain your problem.

Additional context
This may apply to other jet engines, but I'm unsure

[Joey-Destroyah]

p.s.
Could someone please edit the wiki to add info on the new terminal guidance fields?