G++ 4.9.2 and 8.2.0 - final binary's dependency with default lib path searching ./../lib directory

I encountered an odd difference between the binary produced by a 4.9.2 G++ and a 8.2.0 G++ on a Linux, when upgrading from the former to the latter. I was able to narrow it down to the below minimized snippet

//main.cpp
int main(){}

//emptylib.cpp

#!/bin/sh
#to build and verify output
rm -rf bin lib *.o

gcc_bin=/path/to/gcc_4.9.2/bin
#gcc_bin=/path/to/gcc_8.2.0/bin

${gcc_bin}/g++ -B${gcc_bin} -c main.cpp
${gcc_bin}/g++ -B${gcc_bin} -c emptylib.cpp
${gcc_bin}/g++ -B${gcc_bin} -shared emptylib.o -o libemptylib.so
${gcc_bin}/g++ -B${gcc_bin} main.o -o main -L. -lemptylib

mkdir bin
mkdir lib
mv libemptylib.so lib/
mv main bin/

ldd bin/main

The result is a bit strange, because I have provided no -rpath=../lib, but all the same, with the 4.9.2 compiler driver I end up with (in the output of ldd):

libemptylib.so => /path/to/bin/../lib/libemptylib.so

and with 8.2.0

libemptylib.so => not found

the lib does not resolve, as I would expect. I haven't been able to see any documentation that hints at a search for ../lib in any version, but I would not expect this to be a behavior by any version. Was this a bug in 4.9.2 or some earlier version or something that shouldn't have happened in the first place?

As a side note, the 8.2.0 and the 4.9.2 don't have an ld inside of their bin directory (despite me putting the -B in the code snippet), so both compiler drivers are using the /usr/bin/ld (I've verified as much) and producing different results based on the compiler driver alone.