Dynamic library is kept open after dyn.unload

[Lee-Cronin-Fine-NOAA]

I have an issue compiling the cpp file. Specifically, when I compile the cpp file the first time, it runs just fine. However, if I make a change to the cpp file (something as small as adding a space) and then try to recompile it, it won't work. This is what RStudio shows me:

library(TMB)
dyn.unload(dynlib('melba'))
Error in dyn.unload(dynlib("melba")) :
shared object 'C:/Users/lcron/Desktop/melba.dll' was not loaded
compile('melba.cpp')
c:/Rtools/mingw_64/bin/g++ -I"C:/PROGRA1/R/R-3.5.1/include" -DNDEBUG -IC:/Users/lcron/DOCUME1/R/WIN-LI1/3.5/TMB/include -IC:/Users/lcron/DOCUME1/R/WIN-LI1/3.5/RcppEigen/include -DTMB_SAFEBOUNDS -DLIB_UNLOAD=R_unload_melba -DTMB_LIB_INIT=R_init_melba -O2 -Wall -mtune=generic -c melba.cpp -o melba.o
c:/Rtools/mingw_64/bin/g++ -shared -s -static-libgcc -o melba.dll tmp.def melba.o -LC:/PROGRA1/R/R-3.5.1/bin/x64 -lR
[1] 0
dyn.load(dynlib('melba'))
dyn.unload(dynlib('melba'))
compile('melba.cpp')
c:/Rtools/mingw_64/bin/g++ -I"C:/PROGRA1/R/R-3.5.1/include" -DNDEBUG -IC:/Users/lcron/DOCUME1/R/WIN-LI1/3.5/TMB/include -IC:/Users/lcron/DOCUME1/R/WIN-LI1/3.5/RcppEigen/include -DTMB_SAFEBOUNDS -DLIB_UNLOAD=R_unload_melba -DTMB_LIB_INIT=R_init_melba -O2 -Wall -mtune=generic -c melba.cpp -o melba.o
c:/Rtools/mingw_64/bin/g++ -shared -s -static-libgcc -o melba.dll tmp.def melba.o -LC:/PROGRA1/R/R-3.5.1/bin/x64 -lR
C:/Rtools/mingw_64/bin/../lib/gcc/x86_64-w64-mingw32/4.9.3/../../../../x86_64-w64-mingw32/bin/ld.exe: cannot open output file melba.dll: Permission denied
collect2.exe: error: ld returned 1 exit status
[1] 0

If I delete the dll file and try again to recompile the cpp file, it compiles just fine. Interestingly, in order to delete the dll file, I had to close RStudio because I got the following warning when I tried to delete the dll file "The action can't be completed because the file is open in RStudio R Session" Another interesting factor is that this issue only occurs for one specific cpp file. The other cpp files I have created work just fine. Additionally, if I move the cpp file to a separate computer the cpp file compiles fine. I have tried un-installing and re-installing Rtools and TMB. I have also removed admb from my computer since I heard that that can cause problems.

The TMB version I have is 1.7.15
The R version I ave is 3.5.1
Operating System XPS 15 9550