Flashback arresters and oxygen line pressure

Question: One of my students has installed flashback arresters on her
oxy-propane torch, They are mounted at the regulators, not at the

We have noticed that the line pressure in the oxygen hose goes WAY
up when the handset valve is closed. It settles back down to 8 - 10
psi when the valve is open. The propane line appears to be
unaffected. Her “guy” at the welding supply store said that this is
normal with flashback arresters. Her set up wasn’t doing this before
the FA’s were installed. Is this indeed normal, or is it a potential

Emie Stewart