contribute VPE extention AND newby question

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Hello,

I managed to add an important function to LedgerSMB. I don't know how
it's called in English - I would say "packing unit" or "package amount".
In German it is "Verpackungseinheit - VPE". There may be different
partsvendors for a single part and these partsvendors may offer the part
in different packages of different quantities. It was a lot of work. I
had to adjust many functions dealing with $ship and $qty calculations. I
didn't include this in the AR functions, because I'm always going to
sell single pieces or whatever $unit stands for. But for the AP
functions and templates, it is essential because wholesalers normally
sell bigger quantities and packages than I do as a retailer. If you are
interested, I would send you all the changes I made to my currently
installed version 1.2.12. I'm convinced that many users would appreciate
this feature.
I also designed my own LaTeX class derived from German letter. It looks
much better than your standard templates and could serve as an
additional example.

And here comes my question:

I spent a lot of time for reading the source code and trying to grasp
the basic concepts and data structures. I have very little knowledge
about bookkeeping and the meager comments in the source code don't make
it much easier.
What I do not understand is, why does OE->save  delete the orderitems
after &adj_onhand in OE.pm line 310 ? As a result, the TRIGGER
check_inventory removes the corresponding entries from the inventory.
When I enter parts in the Shipping->Receive Form, they appear in the
inventory. After posting the AP invoice, these inventory entries are
deleted - I do not understand this concept or did I find an error. (I
had already observed this behaviour before I changed the sources.)

With kindest regards,

Gerd Nennemann