Updating symlinked packages fails

When I try to overwrite a symlinked package when using the cache option, I get

install.packages("scrm")
[...]
ERROR: ‘scrm’ is not a legal package name

It seems this happens for all front-ends of R CMD INSTALL (I have tested R CMD INSTALL itself, install.packages, update.packages, packrat::install and packrat::install_github).

My best guess is that R tries and fails to overwrite the symlink with a directory. If I manually delete the symlink, everything works. I'm not sure if you can solve this for R CMD INSTALL, but the packrat commands could remove the symlink before installing a new version of an existing package.

sessionInfo()
R version 3.1.2 (2014-10-31)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=de_DE.UTF-8        LC_COLLATE=C               LC_MONETARY=de_DE.UTF-8   
 [6] LC_MESSAGES=en_US.UTF-8    LC_PAPER=de_DE.UTF-8       LC_NAME=C                  LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=de_DE.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
 [1] R6_2.0.1        RCurl_1.95-4.6  Rcpp_0.11.6     XML_3.98-1.1    ape_3.3         assertthat_0.1  bitops_1.0-6    coala_0.0.9106 
 [9] digest_0.6.8    git2r_0.10.1    grid_3.1.2      lattice_0.20-31 magrittr_1.5    memoise_0.2.1   nlme_3.1-119    packrat_0.4.4  
[17] phyclust_0.1-15 rversions_1.0.0 scrm_1.6.0-2    settings_0.2.2  stringi_0.4-1   stringr_1.0.0   tools_3.1.2   

Reproduce the failure with the cache option using install.packages("scrm"), R CMD INSTALL, and the packrat installation commands listed in the report. Start by tracing how an existing symlinked package is handled before installation; done means updating that package no longer reports an illegal package name and does not require manually deleting the symlink.