Based on an analysis of the inherent nodal structures of wavefunctions of 4-boson systems, we found that the inteal energy of the 41+ state should be lower because its structure can be optimized without suffering a strong constraint arising from symmetry (while other 1≤L≤3 states suffer from this kind of constraint). Furthermore,two superior structures favourable in binding are found to be allowed to be possessed by 4+ states. These findings would lead to the appearance of two adjacent 4+ states, as a common feature, in the low-lying spectra of 4-boson systems.