When using a reader conditional, ClojureCL selects the entry with the clj platform key instead of the clr platform key. The issue is on line 142 of the ListReader.cs file. It looks like the platform key code was copied over from the Clojure project without modifying the value for the CLR.
There is also a small, related issue with the changes.md file for version 1.7. The platform keyword is listed as 'cljr' in the changes.md file, but the reader documentation on clojure.org state that the platform key for the CLR is simply 'clr'.
ClojureCLR 1.7 on both Mono on OSX and .NET on Windows 7