Such unattended automatic quantity change events are a big hit on the SB inventories. Say you have handles 1,000 e. and your magento is synced to Quick Books for daily sales reporting. Magento frequently (and for unknown reasons) tend to increase or decrease the qty of "some" items. Our off-shore developers wasn't able to fix this, let along understand the possible coding mistakes that cause the problem. Any ideas are more than welcomed.
By the power of Google, I'm assuming you're using BoostMyShop's "Embedded ERP" extension. If not, you can stop reading here. If so, then have you reviewed their FAQ #10? The TLDR is that these adjustments are expected behavior if (1) you've designated a warehouse as primary, and (2) someone is updating product quantities directly from the Magento product page instead of by an approved method.
If this isn't the source of your trouble, then you'll need to find someone familiar with this extension (or whatever extension you're using). Someone with access to the proprietary code would need to dig deeper since I don't think this is core Magento.
Here's the full FAQ with a link to follow:
10. Unexplained stock movement(s) “Quantity changed event”
This kind of stock movement is created by the Stock discrepancies tool when a product available quantity is not matching the sum of the available qty of all its warehouse available for sales (see Warehouses routing for more explainations about warehouses available for sales).
It usually happens when the product quantity is changed directly from the Magento product page, instead of by creating a stock movement or doing it from any ERP screen.
This occurs only is [sic] you have defined as “Primary” one of your warehouses.
More information : Warehouses configuration
As a reminder, when ERP is installed, product stock quantity should not be updated anymore from the “Qty” field available from each “Magento product view.