Multiple subscripts in combination with curly brackets in LaTeX-based math expressions don't render as expected.

Single underscore with curly brackets works fine: \mathbf{x}_{i,j} = \mathbf{y} renders as $\mathbf{x}_{i,j} = \mathbf{y}$.

Multiple underscores without curly brackets work fine: x_i = y_i renders as $x_i = y_i$.

Multiple underscores with curly brackets fail: \mathbf{x}_{i,j} = \mathbf{y}_{i,j} renders as $\mathbf{x}{i,j} = \mathbf{y}{i,j}$.