It's not so much a liability issue, there are forms and forms to get around that. It used to happen with fair frequency in the past, but as navymich righty points out, the hiccup isn't the reg force keeping out the reserves, it the reserves putting up barriers. I have spoken to several RN officers (exchange officers where I was posted), and some years ago the RNR did a reorganisation; they moved from a model somewhat like what we have -- reservists in reservist positions -- to a model based on "here are the needs, here are the people available and their quals, here's where they go".
Now, the RN training is a little different. One problem in Canada is that we really are training to specific platforms -- reg for a frigate (for the most part), reservist to a MCDV. The RN's training is a little more generic given the large number of different classes of ships they have. So a RNR officer could be in a frigate, a landing ship, an aircraft carrier, a staff HQ, a supply depot, etc. I was at the CF staff college with a RNR officer who was in the Med with a destroyer.
The personnel managers would be very reluctant to send a reserve MARS officer to a frigate, even an ex-reg force "frigate qualified" person (and there's a few out there), as there is a shortage in the MCDVs of watchkeepers right now.
So, the challenge as I see it is that we really have a four-fleet concept: two on each coast, one reg one res. It may sound funny or silly, but the naval reserve, despite being part of the CMS formation, really acts on its own. And, despite the MCDVs on each coast belonging to the fleet commanders, sometimes they act like they are in a different government department. Until we get to a 'one fleet' concept, nothing will change.
You don't get what you don't ask for, but (quite sarcastically) good luck!
Cheers.
