Why is my attempt to use the latest ggmap and R producing a blank map on Windows?

Question

The following two lines of code:

map = get_map()
ggmap(map)

Downloads a ggmapTemp.png:

But produces the following plot:

Why is the successfully saved google map png not getting incorporated into the final ggplot? This is working for us on Mac.

The environment:

sessionInfo()
R version 3.1.2 (2014-10-31)
Platform: x86_64-w64-mingw32/x64 (64-bit)

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    

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

other attached packages:
 [1] mapproj_1.2-2        maps_2.3-6           gdxrrw_0.4.0         rMaps_0.1.1         
 [5] shinyIncubator_0.2.1 rCharts_0.4.5        gridExtra_0.9.1      rgeos_0.3-6         
 [9] knitr_1.6            ggmap_2.3            rgdal_0.8-16         sp_1.0-15           
[13] stringr_0.6.2        shiny_0.9.1          scales_0.2.3         RPostgreSQL_0.4     
[17] DBI_0.2-7            reshape2_1.2.2       RColorBrewer_1.0-5   plyr_1.8.1          
[21] ggplot2_0.9.3.1      gdata_2.13.3         devtools_1.5        

loaded via a namespace (and not attached):
 [1] bitops_1.0-6        caTools_1.16        colorspace_1.2-4    dichromat_2.0-0     digest_0.6.4       
 [6] evaluate_0.5.3      formatR_0.10        gtable_0.1.2        gtools_3.4.1        httpuv_1.3.0       
[11] httr_0.3            labeling_0.2        lattice_0.20-29     MASS_7.3-35         memoise_0.1        
[16] munsell_0.4.2       parallel_3.1.2      png_0.1-7           proto_0.3-10        Rcpp_0.11.1        
[21] RCurl_1.95-4.1      RgoogleMaps_1.2.0.6 rjson_0.2.14        RJSONIO_1.0-3       tools_3.1.2        
[26] whisker_0.3-2       xtable_1.7-3        yaml_2.1.11   

Answer 1

I had the same problem (blank figures from ggmap()), I tried the suggestions from Serban with no luck. I was able to generate figures using a different plotting device:

map=get_map()
bmp('map.bmp')
ggmap(map)
dev.off()

Other devices work as well (tiff, pdf, svg...)