I have not used MALDI-MS, but based my response on much experience with ESI-MS. Since you sampled the reaction mixture directly by MALDI, you will (in general) expect to get an MS response for each organic component of the mixture.
1) I assumed that your desired ester product was formed initially, but had then reacted as shown below,
Ester + HBr ====> Ester/HBr adduct
Ester + H2O ====> Ester/H2O adduct
2) Your mass spectrum might then be expected to give signals for
[Ester/HBr adduct + H]+ (1:1 doublet)
[Ester/H2O adduct + H]+ (singlet)
and the proton-bound dimer,
[Ester/HBr adduct]--- H+ ---[Ester/H2O adduct]
at m/z 507,509 (1:1 doublet).
If you can, please post your MALDI spectrum with the high mass region at ca. m/z 500 clearly resolved.
If not, please post a table of m/z vs. Relative Abundance.