3Com 4050 and D-Link DGS-3324SR spanning tree native vlan

My new place uses a 3Com 4050 as a layer2 core/distribution switch. It's linked to DES-3526, DGS-3324SR and DGS-3100 switches. Protocol of choice is RSTP. Without native/untagged vlan on the links, the following happens:

• 3Com 4050 - DES-3526 - RSTP works okay
• 3Com 4050 - DGS-3100 - RSTP breaks, needs vlan1 untagged
• 3Com 4050 - DGS-3224SR - RSTP breaks, needs vlan1 untagged
• 3Com 4050 - DES-3052P - RSTP breaks, needs vlan1 untagged
• DGS-3224SR - DES3250 - RSTP works okay
• DES-3526 - DES-3052P - RSTP breaks, needs vlan1 untagged
• DGS-3324SR - 3Com 4400 - RSTP works okay

Bottom line: you've gotta love standard implementations of STP...