Sometimes, then I am running meld(); it shows kernel crashed, for example:
{a,b,c,d,e,i,k,m,n,p,q,r,s,t,u,v,w,x,y,z,m#}::Indices(position=independent);
{a,b,c,d,e,i,k,m,n,p,q,r,s,t,u,v,w,x,y,z,m#}::Integer(1..3);
\partial{#}::PartialDerivative.
h_{m? n?}::Metric.
h^{m? n?}::InverseMetric.
h_{m? n?}::Symmetric.
h^{m? n?}::Symmetric.
\delta^{m?}_{n?}::KroneckerDelta.
\delta_{m?}^{n?}::KroneckerDelta.
F_{m? n?}::AntiSymmetric.
\pi::Depends(\partial{#}).
\phi::Depends(\partial{#}).
A_{m?}::Depends(\partial{#}).
h_{m n}::Depends(\partial{#}).
h^{m n}::Depends(\partial{#}).
\psi::Depends(\partial{#}).
\Gamma^{\alpha}_{\mu\nu}::TableauSymmetry(shape={2}, indices={1,2}).
\Gamma^{m}_{n q}::TableauSymmetry(shape={2}, indices={1,2}).
ex := 1/2 h^{a b} F_{n b} \partial_{a}(\pi) \partial_{m}(\psi) (\phi)**2 + 1/2 h^{a b} F_{m b} \partial_{a}(\pi) \partial_{n}(\psi) (\phi)**2-A_{m} \partial_{a}(\phi) \partial_{b}(\pi) \partial_{n}(\psi) \phi h^{a b}-A_{n} \partial_{a}(\phi) \partial_{b}(\pi) \partial_{m}(\psi) \phi h^{a b};
rename_dummies(_);
meld(_);
I'm not sure, but may be it happens only in a case of combination rename_dummies and meld.