While trying to erase (SHIFT+DEL) some big directories (with thousands of files/subdirs inside), it happened many times that 7zFM 9.29a (and previous versions) stops with an error (Directory is not empty) and refuses to continue the job.
On the contrary, Seven's Explorer does almost all the work.
I said "almost", since, i.e., from the compiled boost_1_51_0 folder (the famous C++ library), it left out only an empty boost_1_51_0\libs\format folder.
Note that, at this point, 7zFM itself can erase the boost_1_51_0 folder...
It isn't clear what is happening at Windows level: however, I think 7zFM SHOULD progress with similar erase tasks at least as far as Explorer does!