HDF5 -> H5Ldelete, H5F_FSPACE_STRATEGY_FSM_AGGR and free space - c++

Question

I am facing quite a pickle to understand the space management of HDF5 files.
I have written a code that creates a file that contains a group which contains a series of datasets. The user can decide to remove one or several datasets after they have been added to the file.
This is how I create my HDF5 file:
hid_t fcpl = H5Pcreate(H5P_FILE_CREATE);
hsize_t fsm_size = 0;
H5Pset_file_space_strategy(fcpl, H5F_FSPACE_STRATEGY_FSM_AGGR, 0, fsm_size);
hid_t fapl = H5Pcreate(H5P_FILE_ACCESS);
H5Pset_libver_bounds(fapl, H5F_LIBVER_V110, H5F_LIBVER_LATEST);
H5::H5File data_file(filename, H5F_ACC_TRUNC, fcpl, fapl);
Then, I create a group with:
H5::Group data_group = data_file.createGroup("MyData");
Finally, I add a series of dataset (similar data in this simple case) to this group using:
std::vector<float> array = {1, 2, 3, 4, 5, 6};
for (uint8_t idx = 0; idx < 10; idx++)
{
std::string name = std::string("mydata_") + std::to_string(idx);
hsize_t dims_pol[1] = {array.size()};
H5::DataSpace dataspace_x(1, dims_pol);
H5::IntType datatype_x(H5::PredType::IEEE_F32LE);
H5::DataSet dataset_x;
dataset_x = data_group.createDataSet(name.c_str(), datatype_x, dataspace_x);
dataset_x.write(array.data(), H5::PredType::IEEE_F32LE);
dataset_x.close();
}
Doing so, I do have a file that is filled with the correct data as expected. The (correct from my poor understanding) superblock of the file is:
SUPER_BLOCK {
SUPERBLOCK_VERSION 3
FREELIST_VERSION 0
SYMBOLTABLE_VERSION 0
OBJECTHEADER_VERSION 0
OFFSET_SIZE 8
LENGTH_SIZE 8
BTREE_RANK 16
BTREE_LEAF 4
ISTORE_K 32
FILE_SPACE_STRATEGY H5F_FSPACE_STRATEGY_FSM_AGGR
FREE_SPACE_PERSIST FALSE
FREE_SPACE_SECTION_THRESHOLD 0
FILE_SPACE_PAGE_SIZE 4096
USER_BLOCK {
USERBLOCK_SIZE 0
}
}
The problem arises when I try to delete the datasets. To do that (while the file is still opened), I use the following procedure:
for (uint8_t idx = 0; idx < 10; idx++)
{
std::string name = std::string("mydata_") + std::to_string(idx);
H5Ldelete(data_group.getId(), name.c_str(), H5P_DEFAULT);
}
data_file.close();
From my understanding, the space should be freed when closing the file. However, if the file doesn't contain any reference to the data when opened with the viewer, the size doesn't decrease...
I also tried with unlinking the dataset. This is not working...
Any help would be greatly appreciated...
Thanks