Hi Nick,
Thanks for pointing this out — I put in a fix which should be available by updating the MODEL_SELECTION package to v2.6.1. It does now show an option for loading an input file, however, it also shows a few entries (mcmc, value, hosts) that it should not, and which you can ignore — they should be suppressed with the upcoming BEAST v2.7.4 release that we are testing at the moment. There also may be an issue with the browse button (depending on OS), which may not show all files (also fixed in the next BEAST release).
In short, you might want to consider waiting for the next BEAST release, and then things should work as expected, or, if you are adventurous, you can just update the MODEL_SELECTION package and let me know if that works out.
Cheers,