I get a similar problem with a lot of entities. I think I had this with R2009 (no packs), I assumed it was a graphics issue or a issue just on my installation but yesterday I got a new PC and the problem arose on that one too (R2009 2Packs).
I find that I sometimes get this problem with Corridors and you need to manually rebuild the corridor before it will allow you to select it. It also has happened with alignments, dynamic blocks and a host of other items (that I can't remember all of).
Sometimes a regenall does the trick. It sounds like a bug?
Mike Evans
Civil3D 2022 English
Windows 7 Professional 64-bit
Intel(R) Core(TM) i7-3820 CPU @ 3.60GHz (8 CPUs), ~4.0GHz With 32768MB RAM, AMD FirePro V4900, Dedicated Memory: 984 MB, Shared Memory: 814 MB