I assume that in your case the space occupation continues to grow due to the fact that VMware needs to allocate new slab files to store blocks. This is a typical behaviour of data recovery which tends to allocate all empty space in backup datastore until all the space is claimed (but not necessarly filled).
Reclaim operations are performed to move used memory blocks to continuous locations preventing gaps between blocks which implies that all used memory blocks are moved leaving all free memory block contiguous. This process, I assume, is performed without deallocating slabs so used capacity is continuously marked as growing by data recovery even if actual free space is increased.
KB 1039075 could be useful
...But, I repeat, these are just my assumptions I might be wrong on this...Anyway if this works as in data recovery even if space is marked as 100% used you should be able to keep performing backups since older backup copies are automatically deleted and replaced by new ones.
Regards.