The problem is the same here, I tried T5 mats with T5 tools and T6 mats with T6 tools yesterday. I noticed this problem only in Frostgorge Sound area.
Server: Piken Square (EU)
Zone: Frostgorge Sound
Nodes tried: Cypress sapling, Ancient Sapling, Mithril, Verdant Herbs
Tools used: Orhialcum for T6 and Mithril for T5