I almost got tripped up with this question when I did my Navigation exam last week. The facts were similar, an "odd" magnetic track per the quadrantal rule - with two possible answers fitting that : FL30 and FL50. If one assumed TA was 3,000ft, then with the QNH given (1015) once you wound off the millibars, the height was 2,940ft. This implied that by climbing a further 60ft you'd be at FL30 -the first available FL. This is also the logic used in The Confuser in most of its answers.
In Trevor Thom's books (pg 123 of Vol 6) he implies that you should have AT LEAST 500ft between Transition Altitude and Transition Level. Applying Thom's logic, you'd have to answer FL50. Now I'm not exactly sure where he gets this from (can't see it in the ANO), but it makes good logical sense for vertical separation from those aircraft flying at 3,000ft not in terms of the quadrantal rule.
Anyway - I answered FL30 believing this is what the CAA wanted, and that turned out to be the "correct" answer (Phew!). I personally believe FL50 is a safer option but clearly this is an area of some confusion. Even the two FI's I spoke to after the exam were unsure.
It's like the confusion with "QNH 1000" in RT speak. Trevor Thom says there is a UK exemption which allows this pressure setting to be pronounced wun-tousand. The editor of CAP 413 disagrees and says it is pronounced wun-zero-zero-zero. (My apologies for thread creep).
http://www.airquiz.com/explain/qnh1000.htm