  Galaxy-cluster gravitational lenses enable the study of faint galaxies even
at large lookback times, and, recently, time-delay constraints on the Hubble
constant. There have been few tests, however, of lens model predictions
adjacent to the critical curve (<8") where the magnification is greatest. In a
companion paper, we use the GLAFIC lens model to constrain the Balmer L-sigma
relation for HII regions in a galaxy at redshift z=1.49 strongly lensed by the
MACS J1149 galaxy cluster. Here we perform a detailed comparison between the
predictions of ten cluster lens models which employ multiple modeling
assumptions with our measurements of 11 magnified giant HII regions. We find
that that the models predict magnifications an average factor of 6.2 smaller, a
2-sigma tension, than that inferred from the HII regions under the assumption
that they follow the low-redshift L-sigma relation. To evaluate the possibility
that the lens model magnifications are strongly biased, we next consider the
flux ratios among knots in three images of Sp1149, and find that these are
consistent with model predictions. Moreover, while the mass-sheet degeneracy
could in principle account for a factor of ~6 discrepancy in magnification, the
value of H0 inferred from SN Refsdal's time delay would become implausibly
small. We conclude that the lens models are not likely to be highly biased, and
that instead the HII regions in Sp1149 are substantially more luminous than the
low-redshift Balmer L-sigma relation predicts.
