Yup, for sure. It's a hard problem to fix now. Very hard. It'd be worth doing, but that's not to sell short the scale of the work.
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Why not to just add something like 'dedicated crafting material inventory'? Something where obtained crafting mats would go to, when you buy/gather/monster-droped/quest-rewarded them. Mats used directly from that inventory when crafting. Cannot be dragged to main/retainer/saddle-bag inventory, but can be put on market (from retainer dialog)/sold to vendor/disgarded. Pure server-side - no data send to client, except chat log notice and gathe/drop rnotification. No need in constant client-server syncronization. A lot of space will be cleaned in main inventory, which also will reduce syncronization data.
This crafting materials inventory could even have category tabs for better UI, usability and network bandwidth (logs, minerals, alchemy,cooking, e.t.c) - so not all mats will be requested from server at once, when you open inventory, but only those in active tab.